CHAPTER I

THE NATURE OF THE MINERALS AND THEIR MODE OF OCCURRENCE

The history of the rare earth minerals begins in the year 1751, when the Swedish mineralogist Cronstedt described a new mineral, which he had found intimately mixed with chalcopyrite[1] in the quarry of Bastnäs, near Ryddarhyttan, in the province of Westmannland, Sweden. Cronstedt gave the mineral the name Tung-sten (heavy stone); but as the name Tenn-spat (heavy spar, or heavy mineral) had already been selected by Wallerius (1747) for a new species from Bohemia, believed to contain tin, the choice was not a happy one. More than fifty years after its discovery, a new earth, now known as ceria, was isolated from Cronstedt’s mineral, for which at the same time the name Cerite was proposed.[2] Meanwhile, however, the Finnish chemist Johann Gadolin had observed, in the year 1794, a new earth in a mineral discovered by Arrhenius at Ytterby in Sweden in 1788; he called the new oxide Ytterbia, and the mineral in which he observed it, Ytterbite. The discovery was confirmed in 1797 by Ekeberg, who suggested the names Yttria and Gadolinite for the oxide and mineral respectively; these names were accepted by Klaproth, and soon came into general use.[3] Whilst then Cerite was the first of the rare earth minerals to be discovered, it was in Gadolinite that new elements were first recognised, and the chemistry of the rare earths began in 1794 with Gadolin’s observation.

[1] Chalcopyrite, or Copper pyrites, is a mixed sulphide of iron and copper, of the approximate formula CuFeS₂.

[2] For the history of the name Tungsten, see under the mineral Cerite, Ch. II.

[3] The history of these names will be found somewhat more fully under Gadolinite, Ch. II.

During the nineteenth century a considerable number of rare earth minerals was discovered and analysed; the quantities of the minerals observed, however, were so small that the name ‘Rare earths,’ applied to the new oxides found, was in every sense justified. Until the year 1885, though by that time the scientific interest of the group had been fully demonstrated by the discovery of several new elements, it was supposed that the minerals were almost entirely confined to a few scattered localities in Scandinavia and the Ural mountains. In that year Dr. Auer von Welsbach announced his application of the rare earths to the manufacture of incandescent mantles. Immediately there was a great demand for raw material for the preparation of thoria and ceria. The agents of the Welsbach Company visited all the important mining centres of Europe and America, intent on a search which shortly made it clear that the metals of the so-called ‘rare earths’ are really quite widely distributed in nature. The chief commercial deposits are the monazite sands of the Carolinas, the Idaho basin, and Brazil, the gem-gravels of Ceylon, and the remarkable deposits of gadolinite and allied minerals at Barringer Hill in Texas.

Whilst deposits of commercial importance are not very common, improved scientific methods and more careful search have shown that in traces the rare earths are of exceedingly wide distribution. Sir William Crookes has shown that yttria earths are often present in calcite and in coral; whilst Headden[4] noted that quite considerable amounts (up to 0·03 per cent.) were present in a yellow phosphorescent variety of calcite from Colorado. Similarly Humphreys[5] found that fluorspar usually contains traces of yttrium, whilst one or two phosphorescent varieties contain quantities varying up to 0·05 per cent. The presence of yttria elements in phosphorescent varieties of calcite is interesting, and some connection has been suggested; there is, however, no positive ground for the belief in such a relation.

[4] _Amer. J. Sci._, 1906, [iv.], ~21~, 301.

[5] _Astrophys. J._, 1904, ~20~, 266.

More recently Eberhard[6] has found very considerable quantities of rare earths in cassiterite (tin dioxide, SnO₂) and wolframite [an iron manganese tungstate, (Fe,Mn)WO₄]. A specimen of wolframite from the Erzgebirge was found to contain nearly 0·4 per cent. of rare earths, over half of this quantity being scandium oxide. A process which is readily susceptible of commercial application has been worked out by R. J. Meyer,[7] for the extraction of scandia and the yttria earths from the mixed oxides left after the treatment of wolframite for tungstic acid.

[6] _Sitzungsber. königl. Akad. Wiss. Berlin_, 1908, 851; 1910, 404.

[7] Meyer, _Zeitsch. anorg. Chem._, 1908, ~60~, 134. Meyer und Winter, _ibid._, 1910, ~67~, 398.

Using the spectroscopic method, which is capable of detecting one part of scandia in twenty thousand, Eberhard (_loc. cit._) has found that minute quantities of scandia and yttria earths are present in almost all the commoner rocks and minerals. The minerals richest in scandium were beryl, cassiterite, wolfram, the zircon minerals, and the titanates and columbates of the ceria and yttria oxides. These results are in agreement with the observations of Sir William Crookes,[8] who has made the study of scandium especially his own. From the fact that scandium was often observed unaccompanied by any other member of the rare earth group, Eberhard rather favours Urbain’s conclusion[9] that scandium may not be a member of the rare earth family. Spectroscopic examination has also shown the existence of some of the rare earth elements in the sun and stars (see Europium, p. 189).

[8] _Phil. Trans._ 1910, A, ~210~, 359.

[9] See under Scandium in Pt. II.

In view of this extraordinarily wide distribution of the rare earths in the mineral world, it is but natural that they should be found also in the vegetable and animal kingdoms. Tschernik[10] found 10 per cent. of rare earths in the ash of a coal from Kutais, in the Caucasus, and smaller quantities have been found in the ashes of various plants; members of the group have also been identified in the human body.

[10] See Abstr. in _Zeitsch. Kryst. Min._, 1899, ~31~, 513.

Apart from the general occurrence in traces throughout the mineral kingdom, the minerals in which the rare earths occur are not very common; and though of fairly wide distribution, they are found usually only in small quantities. The earliest known locality, and the most fruitful in regard to number of species, has been the southern part of the Scandinavian peninsula;[11] the minerals occur in the numerous pegmatite veins traversing the granitic country-rock. The mining district round Miask, in the Ural mountains, has also long been known as a fruitful source. Other districts in Europe are the Harz and Erzgebirge, the Laacher See in Prussia, Joachimsthal in Bohemia, Dauphiné, Cornwall, etc. In the United States numerous localities are known; the chief are in the Carolinas and Georgia, Idaho, Oregon, California, Texas, Colorado, Virginia, Pennsylvania and Connecticut. Many of the southern provinces of Brazil also furnish important sources; the famous diamond fields of Minas Geraes, Matto-Grosso, Goyaz and the surrounding provinces yield numerous species, whilst the sands along the southern coasts of Bahia are rich in monazite, and form to-day the most important source of the mineral. Monazite, as well as other rare earth minerals, occurs also in South Africa. An interesting species, plumboniobite (_q.v._), has recently been found in German East Africa. From Australia numerous occurrences are reported, whilst in Canada only a few districts are known to yield members of the group. In Asia important localities are Ceylon--the famous gem-gravels being the most accessible source--and one or two districts in Japan; monazite has been reported recently in considerable quantities near Travancore, India.[12] A more extended search will doubtless show that they occur in many other places.

[11] See Brögger, _Die Mineralien der Süd-Norwegische Granit-Pegmatitgänge_, Christiania, 1906.

[12] _Bull. Imp. Inst._, 1911, vol. ~ix~; No. 2, p. 103.

For several reasons, the rare earth minerals[13] form a group of the highest scientific interest. In the first place, they are generally of very complex composition, more especially with regard to their rare earth content. Thus, whilst it sometimes happens that one or other of the two groups of oxides (the ceria and yttria groups) may predominate to the complete exclusion of the second, it is no uncommon thing for a species to contain almost all the elements of the rare earth family. On the other hand, it is very uncommon for as much as 50 per cent. of the rare earth content to consist of any one oxide. The usual case is that a mineral contains chiefly yttria earths with some ceria earths, or _vice versâ_, the two sub-groups being almost always complex mixtures of several oxides, in which occasionally one may predominate. The remarkable similarity in chemical behaviour of the rare earth elements, and the difficulty of separating them, correspond to this peculiarity in their occurrence.

[13] The phrase ‘rare earth minerals’ will be used whenever it is desired to indicate collectively those minerals of which the yttria and ceria earths form an important constituent, as contrasted to those in which only traces of these oxides occur. Such minerals may often contain titanium, zirconium, or thorium, and, for convenience, the term may be taken to include the commoner zirconium and thorium minerals, but not the commoner titanium minerals.

A second point of even greater interest is that the rare earth minerals are as a general rule strongly radio-active; further, it only occasionally happens that any mineral in which the rare earths do not form an important constituent has more than the feeblest activity; the exceptions being, of course, those uranium minerals which do not contain rare earths. The connection may be pushed even further; for whilst it appears that hardly any rock or mineral possesses absolutely no radio-activity, it is equally worthy of notice that traces of the rare earths, if not quite universal in the mineral world, are yet normally found in the majority of common minerals. As a natural consequence of their activity, the rare earth minerals are also as a rule rich in helium. These facts and the problems which they open up will be treated more fully in a later chapter.

A point of further interest is that of the age of the rare earth minerals. Except in a few cases where they are obviously of secondary formation, these minerals are among the oldest known to us. They occur usually in igneous rocks, particularly in granites which have been considerably metamorphosed. Where erosion has occurred, they are found in deposits of such a nature as to leave very little doubt that the original rock was of plutonic formation and of very considerable age. Whilst it is true, however, that the rare earth minerals are generally of very great antiquity (none of the primary minerals being of more recent date than the palæozoic age), Eberhard has pointed out that the age and nature of common rocks seem to have absolutely no influence on the traces of scandia and yttria oxides which they contain. The geological evidence shows that the rare earth minerals are on the whole exceedingly stable, and that they have been generally formed during the pegmatitic alteration of granites. As early as the year 1840, Scheerer drew attention to these facts, and to the extreme age of the rare earth minerals; but so far his observation seems to have attracted little attention, and no explanation has been put forward.

* * * * *

In the following chapters no attempt is made to treat the rare earth minerals fully. An alphabetical list of all the minerals of any importance which contain rare earths, titanium, zirconium or thorium is given, and of these several are selected for fuller treatment. The basis of selection has been somewhat arbitrary. Those species which are of mineralogical importance, as well as those to which any special historical, scientific or commercial interest attaches, have of course been singled out; in addition, the more recently discovered species have occasionally been considered worthy of separate mention.[14]

[14] A full list of the minerals containing rare earths known up to 1904, with an account of their properties and very full references, will be found in the work of Dr. J. Schilling, _Das Vorkommen der Seltenen Erden im Mineralreiche_, 1904.

It is now being realised that some knowledge of crystallography is essential to the chemist, and for this reason short accounts of the crystallography of the selected types have been given. Apart from this, every effort has been made to render the mineralogy intelligible to the student of chemistry who has devoted no attention previously to this subject, and also to stimulate an interest in the problems of mineral chemistry, unfortunately too often ignored by our present-day teachers. The rare earth minerals afford good examples of some phenomena of great interest to the chemist, as, _e.g._ Isomorphism and Solid Solution, Dimorphism, Isodimorphism, and Molecular Change, and in one or two cases these are treated rather fully.

No special advantages are claimed for the system of classification, which is merely one of convenience. The minerals are divided into five groups:--

(1) The Silicates, which are grouped into three sub-divisions.

(2) The Titano-silicates and the Titanates.

(3) The Tantalo-columbates, sub-divided into those free from titanium and those in which titanium is present.

(4) The Oxides and Carbonates.

(5) The Halides and Phosphates.

A separate chapter has been devoted to the monazite sands, and another to the radio-active properties of the minerals.

ALPHABETICAL LIST OF MINERALS CONTAINING TITANIUM, ZIRCONIUM, THORIUM, OR ELEMENTS OF THE CERIUM AND YTTRIUM GROUPS.

The following list contains all but a few entirely unimportant members of these classes of minerals. The names of those species selected for fuller treatment are printed in heavy type, whilst names of those not so selected, which for convenience are included under the generic term ‘Rare earth mineral,’ _i.e._ roughly all those containing Thorium, or elements of the Cerium and Yttrium groups, and the commoner Zirconium minerals, as distinguished from minerals containing Titanium, are printed in italics. (See footnote on p. 4.) Their properties are given in the following order:--

Chemical Composition and Rare Earth Content. Crystallographic Data. Physical Properties. Locality, etc.

The following contractions are employed:

E = any element or elements of the cerium or yttrium groups. Cer = oxides of the cerium metals. Yttr = oxides of the yttrium metals. G = Specific Gravity. H = Hardness.

Aenigmatite.

A Titanosilicate of Fe´´ and Na, with small proportions of Fe´´´ and Al´´´. Closely allied to the amphiboles. TiO₂ = 7-8%.

Anorthic. Habit prismatic.

G = 3·80-3·86. H = 5¹⁄₂. Black; pleochroism strong.

Greenland and S. Norway.

~Aeschynite~

A Titanocolumbate of Cerium metals, with Th, Fe, Ca, Mn, aq. Cer = 19·4-24·1; Yttr = 1·1-3·1; ThO₂ = 15·7-17·6; TiO₂ = 21-22%.

Rhombic, holosymmetric. Habit prismatic or tabular.

G = 4·9-5·7. H = 5·6. Black; opaque.

Hitterö, Norway; Miask, Urals; also in Germany and Brazil.

~Allanite~ (Orthite).

H₂O, 4R´´O, 3R´´´₂O₃, 6SiO₂, where R´´ = Ca, Fe´´, Be, and R´´´ = Al, Fe´´´, E. An epidote containing rare earths. Cer = 3·6-51 (usually 10-25); Yttr = 0-8 (usually < 3); ThO₂ = 0-3·5%.

Monoclinic; isomorphous with epidote.

G = 3·5-4·2. H = 5¹⁄₂-6. Brown to black; opaque.

Widely distributed in Greenland and Scandinavia.

_Alvite_ (Anderbergite).

Silicate of Zr and E, with Ca, Mg, Be, Al, Cu, Zn, and aq. in small quantities. Cer → 3·98; Yttr → 22; ZrO₂ = 30·5-61·4%.

Tetragonal; optically isotropic. Pseudomorphous after zircon.

G = 3·3-4·3. H = 5-6. Yellowish brown; transparent.

Ytterby, Sweden; Arendal, Norway; various localities in N. America.

~Anatase~ (Octahedrite).

Titanium dioxide. TiO₂ = 97-100%.

Tetragonal; habit octahedral.

G = 3·82-3·95. H = 5¹⁄₂-6. Transparent to opaque; brown to black.

Dauphiné; Bavaria; Cornwall; Norway; Brazil, etc.

_Ancylite._

4Ce(OH)CO₃ + 3SrCO₃ + 3H₂O; with Fe, Mn, Ca, F, traces. Cer = 46·3%.

Rhombic; prismatic.

G = 3·95. H = 4¹⁄₂. Brown; translucent.

Plain of Narsarsuk, Greenland.

_Annerödite._

A parallel growth of Columbite on Samarskite, once believed to be a new species.

Corresponding to Columbite.

Arfvedsonite.

Metasilicate of Na, Ca, Fe´´, Zr; approximately 4Na₂O,3CaO,14FeO,(Al,Fe)₂O₃,21SiO₂. ZrO₂ = 1-6%.

Monoclinic--an amphibole.

G = 3·44. H = 6. Black; pleochroism strong.

S. Greenland and S. Norway.

Arizonite.

Ferric metatitanate, Fe₂O₃,3TiO₂ or Fe₂(TiO₃)₃. TiO₂ = 36·7%.

Uncertain; apparently monoclinic.

G = 4·25. H = 6-7. Dark steel-grey; opaque.

Hackberry, Arizona.

_Arrhenite._

Silico-tantalate of Yttrium metals, with Ce, Al, Fe, Ca, Be, aq. Yttr = 33·2; Cer = 2·6; ZrO₂ = 3·4%.

Amorphous.

G = 3·68. Red; translucent to opaque.

Ytterby, Sweden.

Astrophyllite.

Titano-silicate of Fe, Al, Mn, Zr, K, Na, with aq. ZrO₂ = 1·2-4·5; TiO₂ = 7-14%.

Rhombic. Cleavage (010) perfect.

G = 3·2-3·4. H = 3. Golden to bronze yellow; strongly pleochroic.

Brevik, Norway; El Caso Co., Colorado; Greenland.

_Auerbachite._

An impure hydrated form of Zircon, ZrSiO₄. ZrO₂ = 55·2%.

Tetragonal; isotropic. Pseudomorphous after zircon.

G = 4·06. H = 6. Brownish-grey; translucent to opaque.

Alexandrovsk, Russia.

_Auerlite._

3ThO₂,[3SiO₂,P₂O₅]6H₂O; traces of Fe, Ca, Mg, Al, CO₂, etc. SiO₂ replaced by P₂O₅/3? ThO₂ = 69·2-72·2%.

Tetragonal; probably a pseudomorph after Thorite.

G = 4·4-4·8. H = 2-3. Yellowish to orange-red.

Henderson Co., N. Carolina.

~Baddeleyite.~

ZrO₂, with small amounts of SiO₂, Fe₂O₃, Al₂O₃, CaO, etc. ZrO₂ = 96·5%.

Monoclinic.

G = 4·4-6·0. H = 6¹⁄₂. Brown; pleochroic.

São Paulo, Brazil; Rakwana, Ceylon.

_Bagrationite._

A variety of Allanite (orthite) with no important chemical difference.

Monoclinic; habit prismatic.

G = 3·84. H = 6¹⁄₂. Black; translucent to opaque.

Achmatovsk, Urals.

_Bastnäsite_ (Harmatite).

Hydrated fluocarbonate of Cerium metals, E(F)CO₃. Cer = 64-93·5; ThO₂ = 0-10%.

Hexagonal prisms, pseudomorphous after Tysonite (_q.v._); or massive.

G = 4·9-5·2. H = 4-4¹⁄₂. Yellow to brown; transparent.

Bastnäs, Sweden; Pike’s Peak, Colorado.

~Beckelite.~

Zirconosilicate of rare earths and lime, Ca₃E₄(Si,Zr)₃O₁₅. Cer = 59·7; Yttr = 2·8; ZrO₂ = 2·5%.

Cubic, in octahedra and dodecahedra. Cubic cleavage.

G = 4·15. Brown; transparent.

Near Sea of Azov, Russia.

Benitoite.

A Titano-silicate of barium, BaTiSi₃O₉. TiO₂ = 20·1%.

Rhombohedral.

H = 6¹⁄₂-7. Colourless to blue; transparent; pleochroism strong.

Source of San Benito River, California.

~Blomstrandine.~

Dimorphous with Polycrase (_q.v._), and of same composition.

Orthorhombic; isomorphous with priorite (_q.v._).

G = 4·5-5·0; H = 6¹⁄₂. Bright black; translucent.

Hitterö and Arendal, Norway.

Blomstrandite.

Hydrated titano-columbate of U, with some Fe and Ca. TiO₂ = 10·7%.

Massive.

G = 4·17-4·25. H = 5¹⁄₂. Black; opaque.

Nohl, Sweden.

_Bodenite._

A variety of Allanite (_q.v._), rich in Al and Ca, with no Be. Yttr = 17; Cer = 18%.

Monoclinic.

As Allanite.

Boden, near Marienburg.

_Britholite._

A basic phosphosilicate of cerium metals, with Fe, Ca, Mg, Na, F. Cer = 60·5-60·9%.

Hexagonal; habit prismatic.

G = 4·446. H = 5¹⁄₂. Brown; transparent.

Naujakasik, Greenland.

_Bröggerite._

A variety of Uraninite (_q.v._), with rare earths, Th, Pb, Fe, Ca, Si, aq., etc. Cer = 0·4; Yttr = 1·4-4·3; ThO₂ = 4·7-6·1%. Traces of ZrO₂.

Cubic, in octahedra and dodecahedra.

G = 8·7-9·0. H = 5-6. Black; translucent to opaque.

Anneröd, near Moos, Norway.

~Brookite.~

Titanium dioxide, TiO₂ = 99-100%; trimorphous with Anatase and Rutile.

Orthorhombic.

G = 3·87-4·01. H = 5¹⁄₂-6. Brown; opaque.

Dauphiné; Urals; Switzerland; Magnet Cove, Arkansas.

_Calciothorite._

A variety of Thorite containing lime--5ThSiO₄,2Ca₂SiO₄ + 10H₂O. ThO₂ = 59·3%.

Completely amorphous.

G = 4·114. H = 4¹⁄₂. Deep red; translucent.

Islands of Läven and Arö, Langesund Fiord, Norway.

_Cappelenite._

A borosilicate of rare earth metals and barium, with traces of Th, Ca, K, Na, aq. Approximately BaSiO₃, YBO₃. Cer = 4·2; Yttr = 52·5%.

Hexagonal; habit prismatic.

G = 4·407. H = 6-6¹⁄₂. Greenish brown; translucent.

Island of Klein-Arö, Langesund Fiord, Norway.

_Caryocerite_ (Karyocerite).

Complex fluosilicate of E, with Ta, Th, Ca; also CO₂, P₂O₅, B, Al, Fe, Mn, U, Mg, Na, aq., etc. Approaching Melanocerite, (_q.v._), but richer in Th. Very complex. Cer = 41·8; Yttr = 2·2; ThO₂ = 13·6; ZrO₂ = 0·5%.

Rhombohedral, but isotropic; apparently a pseudomorph after Melanocerite (_q.v._)

G = 4·295. H = 5-6. Nut brown; translucent. Faces very brilliant, but striated. Lustre vitreous to resinous.

Various rocks and shoals round Arö Island, Langesund Fiord, Norway.

_Castelnaudite._

A variety of Xenotime (_q.v._) containing Zr. Yttr = 60·4; ZrO₂ = 7·4%.

Tetragonal.

G = 4·5. H = 4-5. Greyish white to pale yellow.

Diamond sands of Brazil.

_Cataplejite_ (Kataplejite).

H₄(Na₂,Ca)ZrSi₃O₁₁. ZrO₂ = 29·6-40% (usually 30-33%).

Monoclinic, pseudohexagonal. Becomes truly hexagonal at 140°C.

G = 2·8. H = 6. Yellow to brown; transparent to opaque.

A blue variety is known which contains no calcium.

Islands of Langesund Fiord, Norway; Narsarsuk, Greenland.

~Cerite.~

A basic silicate of Cerium metals, with Ca and Fe. Approximately H₃(Ca,Fe)Ce₃Si₃O₁₃. Cer = 50·7-71·8%. In a variety from Batoum, Tschermak reports Yttr = 7·6 and ZrO₂ = 11·7%.

Orthorhombic; usually massive or granular.

G = 4·9. H = 5-6. Brown to red; translucent to opaque.

Ryddarhyttan, Sweden; Batoum, Caucasus?

_Chalcolamprite._

A silico-columbate of E, Zr, Ca, Fe, Na, K; R₂Cb₂F₂SiO₉, where R represents various metals. E = 3·41; ZrO₂ = 5·7%.

Cubic, in small octahedra.

G = 3·77. H = 5¹⁄₂. Greenish brown; opaque. Metallic lustre (χαλκός = Copper, λαμπρός = lustre).

Narsarsuk, S. Greenland.

_Churchite._

Hydrous phosphate of Cerium metals and Ca; Cer = 51·87%.

Monoclinic? Allegations only.

G = 3·14. H = 3¹⁄₂. Greyish; transparent to translucent.

Cornwall.

_Cleveite._

A variety of Uraninite (_q.v._) rich in rare earths and helium. Cer = 2·3-2·9; Yttr = 10·0-10·3; ThO₂ = 4·6-4·8%.

Cubic; usually massive.

G = 7·49. H = 5¹⁄₂. Black; opaque.

Arendal, Norway.

~Cordylite.~

Fluocarbonate of Cerium metals and Ba; E₂F₂Ba(CO₃)₃. Cer = 49·4%.

Hexagonal; isomorphous with Parisite (_q.v._).

G = 4·31. H = 4¹⁄₂. Yellow; transparent.

Plain of Narsarsuk, Greenland.

Cossyrite.

A variety of Aenigmatite (_q.v._) of very complex composition, TiO₂ = 6-8%.

Anorthic.

G = 3·74. H = 5. Black; opaque.

Island of Pantellaria (formerly Cossyra).

_Cyrtolite._

A pseudomorph after zircon, allied to Alvite (_q.v._).

Tetragonal.

_See_ Alvite.

Various localities in Scandinavia, and U.S.A.

_Davidite._

A Titanate of Fe, U, V, Cr, and E--uncertain formula. TiO₂ > 50; E₂O₃ = 5-10%.

Cubic--in grains and rounded crystals.

G = 4 about. Black, with brilliant lustre.

Olary, S. Australia.

~Delorenzite.~

2FeO,UO₂,2Y₂O₃,24TiO₂. Yttr = 14·63; TiO₂ = 55%.

Rhombic; habit prismatic.

G = 4·7. H = 5¹⁄₂-6. Black; translucent to opaque; lustrous.

Craveggia, Piedmont, Italy.

Derbylite.

FeO,Sb₂O₅ + 5FeO,TiO₂? TiO₂ = 35% about.

Orthorhombic; habit prismatic.

G = 4·53. H = 5. Pitch black; opaque; lustre resinous.

Tripuhy, Minas Geraes, Brazil.

Dysanalyte (Perovskite).

Approximately 6RTiO₃,R(Cb,Ta)₂O₆, where R = Ca, Fe´´. Believed by Hauser to be merely an impure Perovskite (_q.v._). Cer = 0-5·1; TiO₂ = 41·5-59·3%.

Cubic.

G = 4·13. H = 5-6. Black; opaque.

Vogtsburg, near Baden, Germany.

Elpidite.

Na₂Zr(Si₂O₅)₃, 1¹⁄₂H₂O. ZrO₂ = 20·5%.

Orthorhombic.

G = 2·52-2·56. H = 7-8. Colourless to red; translucent.

Various localities in Greenland.

_Endeiolite._

R´´Cb₂O₆(OH)₂ + R´´SiO₃ (cf. Chalcolamprite). E₂O₃ = 4·43; ZrO₂ = 3·78%.

Cubic.

G = 3·44. H = 4. Dark chocolate-brown; transparent.

Narsarsuk, Greenland.

_Erdmannite_ (Michaelsonite).

A silicate of E and Ca, with Zr, Be, Th, Al, Fe, aq., etc. An altered Homilite? Cer = 17·7-34·9; Yttr = 1·4-2·1; ThO₂ + ZrO₂ = 0-12%.

Amorphous; isotropic.

G = 3·01-3·39. H = 4¹⁄₂. Brown to leek-green.

Near Brevig, Norway.

_Erikite._

A phosphosilicate of E, Ca, Al, K and Na, with ThO₂, H₂O, etc. Cer = 40·5; ThO₂ = 3·3%.

Orthorhombic.

G = 3·473. H = 5¹⁄₂-6. Brown; opaque.

Julianehaab, Greenland.

~Eucolyte.~

R´₄R´´₃Zr(SiO₃)₇, where R´ = K, Na, H, and R´´ = Ce(OH), Fe, Mn, Ca, and Zr(OCl) may replace SiO₂? A very complex mineral. ZrO₂ = 10·9-20; Cer = 0-5·2%.

Rhombohedral.

G = 3·0-3·1. H = 5-5¹⁄₂. Red to brown; translucent. Double Refraction strong, -ve.

Various localities in Norway.

_Eucrasite._

An altered Thorite (_q.v._) containing E, Ca, Fe, Mn, Na, Ti, H₂O, etc. Cer = 14; Yttr = 5·9; ThO₂ = 36·0; ZrO₂ = 0·6%.

Rhombic (Paijkull). Amorphous, isotropic (Brögger).

G = 4·39. H = 4¹⁄₂-5. Brownish black; opaque.

Near Brevig, Norway.

~Eudialite.~

A variety of Eucolyte (_q.v._) of the same composition.

As Eucolyte.

G = 2·92. Double Refraction strong, +ve. Otherwise as Eucolyte.

Greenland; Lapland; Arkansas, U.S.A.

~Euxenite.~

E(CbO₃)₃,E₂(TiO₃)₃,1¹⁄₂H₂O; with U and Zr. Cer = 2·3-8·4; Yttr = 13·2-34·6; TiO₂ = 20-23%. ThO₂ + ZrO₂ usually in traces.

Orthorhombic; usually massive.

G = 4·6-5·0. H = 6¹⁄₂. Brownish-black; translucent to opaque.

Hitterö, Brevig, Jolster, Arendal, Norway; Cooglegong, Australia; N. Carolina.

~Fergusonite.~

Approximately E₂O₃, (Cb,Ta)₂O₅, with U, Fe, Ca. Cer = 0·5-13·9; Yttr = 27·9-47·1; ThO₂ + ZrO₂ = 0-7%. [Berzelius found Cer = 36·3; Yttr = 0% in one specimen.]

Tetragonal, polar.

G = 5·84-4·3 when largely hydrated. H = 5·6. Brown to black.

Norway; Australia; Texas, etc.

_Florencite._

A silico-phosphate of E and Al. Cer = 28% approximately.

G = 3·6. H = 5. Yellow to red. Resinous lustre.

Minas Geraes and diamond localities in Brazil.

_Fluocerite._

Basic fluoride of rare earth metals, E₂O₃,4EF₃. Cer = 81·4-82·6; Yttr = 1·1-4·3%.

Massive. Original hexagonal mineral of Berzelius and Haidinger, probably Tysonite (_q.v._).

G = 5·7-5·9. H = 4. Reddish yellow; opaque.

Österby, Sweden.

_Freyalite._

Silicate of E and Th, with Al, Fe, Mn, Na, aq., etc. Cer = 31·3; ThO₂ = 28·4; ZrO₂ = 6·3%.

Amorphous.

G = 4·06-4·17. H = 6. Brown; opaque; lustre resinous.

Brevig, Norway.

~Gadolinite.~

FeO, 2BeO, Y₂O₃, 2SiO₂, where Y = yttrium metals. Cer = 3·4-51·5 (usual 6-20); Yttr = 5-60 (usual 35-48)%.

Monoclinic; habit prismatic. Often amorphous and isotropic.

G = 4·0-4·5. H = 6¹⁄₂-7. Brown and green. Double Refraction strong, +ve.

Ytterby and Fahlun, Sweden; Hitterö and Malö, Norway; Llano Co., Texas; Colorado, etc.

Geikielite.

(Mg,Fe´´)TiO₃. TiO₂ = 56·1-64·8%. Specimens rich in iron are called Picroilmenite.

Massive.

G = 4 about. H = 6. Purplish or brownish black.

Ceylon.

Gorceixite.

An alumino-phosphate of alkaline and ceria earths. Cer = 0-3%.

Microcrystalline.

G = 3. H = 6. White to brown. Translucent.

Diamond sands of Brazil.

Guarinite.

Formerly supposed to be dimorphous with Titanite (_q.v._); shown by Zambonini and Prior (1909) to be identical with Hiortdahlite (_q.v._).

Hainite.

Tantalo-silicate and titanate of Zr, Ca, Na. ZrO₂ = 29-32%.

Anorthic.

G = 3·2. H = 5. Colourless to yellow; transparent.

Bohemia.

~Hellandite.~

3H₂0, 2R´´O, 3R´´´₂O₃, 4SiO₂, where R´´ = Ca, Mg, Th/2; R´´´ = E, Al, Fe, Mn. E₂O₃ = 40%.

Monoclinic; habit prismatic.

G = 3·70. H = 5¹⁄₂. Reddish-brown when fresh.

Lindvikskollan and Kragerö, Norway.

Hiortdahlite.

3CaSiO₃,Ca(F,OH)NaZrO₃. ZrO₂ = 21·5; TiO₂ = 1·5%.

Anorthic; habit tabular.

G = 3·27; H = 5-5¹⁄₂. Yellow, with weak pleochroism.

Island of Läven, Langesund Fiord, Norway.

_Hjelmite_ (Hielmite).

A stanno-tantalate of Ca, Mn, Fe, E, related to Yttrotantalite (_q.v._). E₂O₃ = 1-6%.

Orthorhombic.

G = 5·82. H = 5. Black; lustre metallic.

Fahlun, Sweden.

Homilite.

(Ca,Fe)₃(BO)₂(SiO₄)₂. Sometimes with ceria earths, 0-2·6%.

Monoclinic--isomorphous with Gadolinite (? Brögger).

G = 3·34-3·38. H = 4¹⁄₂-5. Black; pleochroic.

Islands of Lanegsund Fiord, Norway.

_Hussakite_ (Xenotime).

A prismatic form of Xenotime (_q.v._), erroneously supposed to contain > 6% SO₃.

Diamond sands of Brazil.

Hydrotitanite.

An altered Perovskite (_q.v._) with Fe´´´ and aq. TiO₂ = 82·8%.

Amorphous.

G = 3·68. H = 1-2. Yellowish grey.

Magnet Cove, Arkansas.

~Ilmenite.~

FeTiO₃; composition varies widely. TiO₂ = 3·5-52·3%.

Rhombohedral.

G = 4·5-5. H = 5-6. Black; opaque. Slightly magnetic.

Norway; Dauphiné; Bohemia; Cornwall, etc.

Ilmenorutile.

FeO,Nb₂O₅,5TiO₂? TiO₂ = 66-75%.

Tetragonal, very near to Rutile (_q.v._).

G = 4·3-5·0. H = 6-7. Brown to black; opaque.

Ilmen Mountains, Russia.

_Johnstrupite._

Silico-titanate of E, Al, Mg, Ca, Na, etc., with F and aq. Cer = 13·5; Yttr = 1·1; TiO₂ = 7-8; ThO₂ + ZrO₂ = 3·6%.

Monoclinic, very close to Epidote.

G = 3·19-3·29. H = 5. Brownish green; weakly pleochroic.

Islands of the Langesund Fiord, Norway.

_Kainosite_ (Cenosite).

CaY₂(SiO₃)₄,CaCO₃,2H₂O, where Y = Yttrium metals. Yttr = 30-37%.

Uncertain; pseudo-hexagonal.

G = 3·38-3·41. H = 5-6. Yellowish brown.

Hitterö and province of Nordmark, Norway.

~Keilhauite~ (Yttrotitanite).

An isomorphous mixture of Titanite (_q.v._) with (E,Al,Fe)SiO₅. E₂O₃ = 5-12; TiO₂ = 26-30%.

Monoclinic; isomorphous with Titanite.

G = 3·52-3·77. H = 6¹⁄₂. Brown to black.

Various localities in Norway.

_Kischtimite._

A fluocarbonate of the Cerium metals, near Parisite (_q.v._). Cer = 74·2%.

Massive.

G = 4·78. H = 4¹⁄₂. Yellowish brown; translucent.

Barsovka River, Kyshtymsk, Urals.

_Knopite._

A variety of Perovskite (_q.v._) containing E and Fe. Cer = 4-7; TiO₂ = 55%.

Pseudo-cubic.

G = 4·2. H = 5¹⁄₂. Grey; opaque; lustre metallic.

Alnö, Sweden.

_Kochelite._

A columbate of E, Fe, Zr; with ThO₂, SiO₂, Ca, aq., etc. Allied to Fergusonite (_q.v._). Yttr = 17·22; ZrO₂ = 12·8; ThO₂ = 1·23%.

Doubtful; may be tetragonal.

G = 3·74. H = 3-3¹⁄₂. Brown to honey yellow; translucent.

The Kochelweise, near Schreiberhau, Silesia.

_Koppite._

Columbate of E, Ca, Fe, Th, K, Na, etc. Near Pyrochlore (_q.v._). Cer = 4-10; ZrO₂ = 0-5%.

Cubic; in dodecahedra.

G = 4·45-4·46. H = 5-6. Brown; transparent.

Schelingen, Black Forest Mountains, Germany.

~Lanthanite.~

Hydrated carbonate of Cerium metals, especially La; E₂(CO₃)₃,9aq. Cer = 54·9%.

Orthorhombic; habit tabular.

G = 2·6-2·7. H = 2. White; opaque.

With Cerite (_q.v._) at Bastnäs, Sweden; Bethlehem, Pennsylvania, U.S.A.

Lavenite.

(Mn,Ca,Fe)(ZrOF)Na(SiO₃)₂? ZrO₂ = 28·8-31·6%.

Monoclinic; habit prismatic.

G = 3·51-3·55. H = 6. Brown to yellow; translucent.

Langesund Fiord, Norway; the Ardennes, France.

Leucosphenite.

BaO,2Na₂O,2(Ti,Zr)O₂,10SiO₂. TiO₂ = 13·2; ZrO₂ = 3·5%.

Monoclinic; wedge-shaped.

G = 3·05. H = 6¹⁄₂. White; transparent.

Narsarsuk, Greenland.

Lewisite.

3R´´Sb₂O₆,2R´´TiO₃, where R = Ca, Fe´´ and Mn. TiO₂ = 11-12%.

Cubic; in small octahedra.

G = 4·95. H = 5¹⁄₂. Yellow to brown; translucent.

Tripuhy, Minas Geraes, Brazil.

_Loranskite._

Tantalate of E, Zr, Fe, etc. Yttr = 10; Cer = 3; ZrO₂ = 20%.

Massive.

G = 4·6. H = 5. Black; opaque. Metallic lustre.

Finland.

Lorenzenite.

Titano-silicate of Na and Zr; TiO₂ = 35; ZrO₂ = 12%.

Orthorhombic; acicular.

G = 3·4. H = 6. Colourless; transparent.

South Greenland.

_Mackintoshite._

Mixture of oxides, chiefly of Th and U; also Fe, Ca, Mg, Pb, Na, B, Ta, etc. Composition very complex. ThO₂ = 45·3; E₂O₃ = 1·9; ZrO₂ = 1%.

Tetragonal, resembling thorite (_q.v._).

G = 5·42. H = 5¹⁄₂. Black; opaque.

Bluffton, Llano Co., Texas.

_Malacone._

An altered Zircon (_q.v._), with E, Ca, Fe, H₂O, etc. ZrO₂ = 47-67%.

Tetragonal; pseudomorphous.

G = 3·9-4·1. H = 6. Brown, often dull white internally.

Hitterö, Norway; Haute Loire, France; and in U.S.A.

Mauzeliite.

Very similar to Lewisite (_q.v._), with Pb. TiO₂ = 8%.

Cubic.

G = 5·11. H = 5-6. Brown; translucent.

Jakobsberg, Sweden.

_Melanocerite._

Very complex fluosilicate of E and Ca, chiefly. Cer = 48; Yttr = 9·2; ThO₂ + ZrO₂ = 2%.

Rhombohedral; habit tabular.

G = 4·13. H = 5-6. Deep brown to black. Transparent.

Langesund Fiord, Norway.

_Microlite._

Complex columbate of Ca, E, Fe, etc., with F and H₂O. E₂O₃→ 8%.

Cubic; habit octahedral.

G = 5·48-5·56. H = 5-5¹⁄₂. Red to yellow.

Stockholm, Sweden; Island of Elba; and in U.S.A.

Molengraafite.

Titano-silicate of Ca, Na, Fe, Al, Mn, etc. TiO₂ = 28%.

Monoclinic; in small prisms.

Yellow. High refraction and birefringence.

Pilandsberg, Transvaal.

~Monazite.~

Phosphate of E, with Th and SiO₂. Cer = 49-74; Yttr = 1-4; ThO₂ = 1-20%.

Monoclinic.

G = 4·9-5·3. H = 5-5¹⁄₂. Red to brown and yellow; translucent.

The Carolinas; Idaho; Brazil; Scandinavia, etc.

_Mosandrite._

In composition identical with Johnstrupite (_q.v._).

Isomeric with Johnstrupite (_q.v._).

G = 2·93-3·03. H = 4. Reddish brown; translucent.

Langesund Fiord, Norway.

_Muromontite._

A variety of Allanite (_q.v._), rich in yttria earths and Be, but poor in Al and ceria earths. Cer = 9·1; Yttr = 37·1%.

_See_ Allanite.

G = 4·263. H = 7. Black to greenish black.

Mauersberg, Erzgebirge, Saxony.

~Naegite.~

A silicate of Zr, ZrSiO₄, with E, Th, U, Cb, etc. ZrO₂ = 55·2; Yttr = 9·12; ThO₂ = 5·01%.

Tetragonal; in globular aggregates.

Gr = 4·091. H = 7¹⁄₂. Dark green or brown; dull.

Gravel-tin of Japan.

Narsarsukite.

Na₆FeTi₂Si₁₂O₃₂F. TiO₂ = 14%.

Tetragonal. Habit tabular.

Gr = 2·75. H = 7-7¹⁄₂. Yellow to reddish-brown; pleochroic.

Plain of Narsarsuk, Greenland.

Neptunite.

(K,Na)₂(Fe,Mg,Ca,)₂(Ti,Si)₄O₁₂. TiO₂ = 18%.

Monoclinic. Habit prismatic.

G = 3·23. H = 5¹⁄₂. Black, red in flakes. Translucent to opaque.

Narsarsuk, Greenland.

_Nivenite._

A variety of Cleveite (_q.v._), readily soluble in dilute acids.

Cubic; crystallisation indistinct.

G = 8·01. H = 5¹⁄₂. Velvet black; opaque.

Bluffton, Llano Co., Texas.

_Nohlite._

A variety of Samarskite (_q.v._) containing water (→ 4·6%).

Massive, without cleavage.

G = 5·04. H = 4¹⁄₂-5. Brownish black; opaque.

Nohl, near Kongelf, Sweden.

_Oerstedite._

A variety of Zircon (_q.v._), poor in SiO₂. ZrO₂ = 69%.

Tetragonal; angles exactly those of Zircon.

G = 3·629. H = 5¹⁄₂. Reddish-brown; adamantine lustre.

Arendal, Norway.

~Orangite.~

ThSiO₄, usually with Fe, Ca, H₂O in traces. ThO₂ = 71·2-73·8%.

Tetragonal. Habit prismatic.

G = 5·19-5·40. H = 4¹⁄₂-5. Orange yellow; lustrous.

_See under_ Thorite.

~Parisite.~

E₂CaF₂(CO₃)₃. Cer = 50·8-64·4; Yttr = 0-2·5%.

Hexagonal. Habit pyramidal.

G = 4·36. H = 4¹⁄₂. Yellow to red; transparent.

Muso Valley, Columbia; Montana, U.S.A.; Greenland; Norway; the Urals, etc.

Perovskite.

CaTiO₃, with traces of Fe´´. TiO₂ = 58·9%.

Pseudo-cubic? Optically biaxial.

G = 4·017. H = 5¹⁄₂. Yellow; transparent to opaque.

The Urals; Switzerland; Tyrol, etc.

_Pilbarite._

PbO,UO₃,ThO₂,2SiO₂,2H₂0 + 2aq. ThO₂ = 31·3%. Cer and Yttr--traces.

Amorphous.

G = 4·4-4·7. H = 2¹⁄₂-3. Bright yellow; opaque.

Pilbara goldfields, West Australia.

_Pitchblende._

A mixture of oxides, chiefly UO₂ and UO₃, but without E₂O₃ or ThO₂.

Amorphous.

G = 5-6·5. H = 3-4. Black; resinous lustre.

Bohemia; Cornwall; Carolina; Norway, etc.

_Plumboniobite._

A variety of Samarskite (_q.v._) containing Pb; R´´₂Cb₂O₇, R´´´₄(Cb₂O₇)₃, where R´´ = Fe, Pb, Ca, UO, R´´´ = E, Al. Yttr = 14·3%.

Massive, isotropic.

G = 4·80-4·81. H = 5-5¹⁄₂. Dark brown to black.

Morogoro, Uluguru Mountains, German E. Africa.

~Polycrase.~

A titano-columbate of E and U; Yttr = 19·5-32·5; TiO₂ = 25-33%. Cer and ThO₂ traces. Isomorphous with Euxenite.

Orthorhombic.

G = 4·0-4·8. H = 6. Black; vitreous lustre.

Norway.

~Priorite.~

Dimorphous with Euxenite (_q.v._).

Orthorhombic; isomorphous with Blomstrandine.

G = 4·6-5·0. H = 6. Black; transparent in flakes.

Swaziland, S. Africa.

Pseudobrookite.

Fe₄(TiO₄)₃, ferric orthotitanate. TiO₂ = 44-53%.

Orthorhombic.

G = 4·39-4·98. H = 6. Dark brown to black.

Norway; France.

_Pyrochlore._

A columbate of Ca and E, with Th, Fe, Ti, F, etc. E₂O₃ → 18; TiO₂ = 5-14%.

Cubic.

G = 4·2-4·36. H = 5-5¹⁄₂. Dark brown.

Scandinavia; the Urals; Tasmania, etc.

Pyrophanite.

MnTiO₃, with traces of SiO₂. TiO₂ = 50-53%.

Rhombohedral; isomorphous with Ilmenite.

G = 4·537. H = 5. Deep blood-red; translucent; lustrous.

Pajsberg, Sweden.

_Retzian._

Hydrated arsenate of Mn´´, Ca, E. Cer + Yttr = 8-11%.

Orthorhombic, usually in prisms.

G = 4·15. H = 4. Brown; pleochroic; transparent.

Province of Nordmarken, Sweden.

_Rhabdophane_ (Scovillite).

Hydrated phosphate of E, Al, Fe, Mg, etc., with SiO₂. Cer = 53·8-57; Yttr = 2·1-10·0%.

Massive.

G = 3·94-4·01. H = 3¹⁄₂. Brown to yellow; translucent.

Cornwall; Scoville, Connecticut, U.S.A.

Rhönite.

(Na,K,H)₃Ca₃(Fe´´,Mg)₁₅(Al,Fe´´´)₁₆(Si,Ti)₂₁O₉₀. TiO₂ = 9·5%.

Anorthic, isomorphous with Aenigmatite.

G = 3·5-4·3. Brown, with strong pleochroism.

Rhön Mountains, Saxony.

_Rinkite._

A titanosilicate closely allied to Mosandrite and Johnstrupite (_q.v._)--Na₉Ca₁₁Ce₃(Ti,Th)₄₁Si₁₂O₄₆? Cer = 21; Yttr = 0·4-1·4; TiO₂ = 13-14%.

Monoclinic, very close to Johnstrupite.

G = 3·46. H = 5. Yellow, pleochroic; translucent.

Kangerdluarsuk, Greenland.

~Risörite.~

An yttria columbate, near Fergusonite, but with no U and considerable TiO₂; Yttr = 37; Cer = 2·9-4·0; TiO₂ = 6·5%.

No data yet determined. Isotropic.

G = 4·179. H = 5¹⁄₂. Yellowish brown.

Norway.

_Rogersite._

Hydrated yttria columbate. Yttr = 60·12%. A weathered Samarskite?

Amorphous, mamillary.

G = 3·313. H = 3¹⁄₂. White.

Mitchell Co., N. Carolina.

_Rosenbuschite._

Titanosilicate of Ca, Zr, Na, E, Fe, Mn, with F. ZrO₂ = 18·7-20; Cer = 0·3-2·4%.

Monoclinic, in spherical aggregates.

G = 3·30-3·31. H = 5-6. Orange-grey.

Near Brevik, Sweden.

_Rowlandite._

Silicate of E, with Th, Ti, Fe, etc.--2Y₂O₃, 3SiO₂. Cer = 14·4; Yttr = 47·7; ThO₂ = 0·6%.

Massive.

G = 4·515. H = 6. Pale dull green.

Llano Co., Texas.

~Rutile.~

Titanium dioxide; TiO₂ = 98-100%

Tetragonal; habit prismatic.

G = 4·18-4·25. H = 6-6¹⁄₂. Reddish-brown to black.

Very widely in Europe and America.

~Samarskite.~

R´´₃R´´´₂(Cb,Ta)₆O₂₁, where R´´ = Fe, Ca, UO₂; R´´´ = E. Cer = 1·2-6·4; Yttr = 4·72-21·2; ThO₂ + ZrO₂ → 7%.

Orthorhombic; usually massive.

G = 5·6-5·8. H = 5-6. Deep velvet black; opaque.

Miask; Urals; Mitchell Co., N. Carolina.

Schorlomite.

A titaniferous Garnet--3CaO,(Fe,Ti)₂O₃,3(Si,Ti)O₂. TiO₂ = 12·5-22%.

Cubic; usually massive.

G = 3·81-3·88. H = 7-7¹⁄₂. Black; transparent in flakes.

Magnet Cove, Arkansas.

Senaite.

(Fe,Mn,Pb)O,TiO₂, cf. Ilmenite. TiO₂ = 49-52%.

Rhombohedral; isomorphous with Ilmenite, Geikielite, etc.

G = 5·3 (to 4·2 when weathered). H = 6¹⁄₂. Black.

Diamantina, Minas Geraes, Brazil.

~Sipylite.~

Columbate of E, Zr, Fe, U, Sn, etc.; near Fergusonite (_q.v._).

Cubic, in octahedra. Usually granular.

G = 4·89. H = 6. Brownish-black; translucent.

Amhurst Co., Virginia.

_Steenstrupine._

A silicate of E, Fe, Na, Th, Mn, Al, Ti, H₂O, etc.; near Melanocerite. Cer = 14·4-32·5; Yttr = 0-15·9; ThO₂ = 2·1-7·1%.

Rhombohedral.

G = 3·38. H = 4. Brown; faces dull.

Kangerdluarsuk, Greenland.

Strüverite.

FeO,(Nb,Ta)₂O₅,4TiO₂. TiO₂ = 69-71%.

Tetragonal; angles very close to those of rutile.

G = 5·0. H = 6-7. Black; opaque.

Craveggia, Piedmont, Italy; and in Madagascar.

_Tachyaphaltite._

An altered zircon, containing H₂O. ZrO₂ = 40-50%.

Tetragonal; very close to Zircon.

G = 3·6. H = 5¹⁄₂. Dark brown.

Kragerö, Norway.

_Tengerite._

Hydrated carbonate of E, Be, Ca, etc.; a weathered Gadolinite (_q.v._). E₂O₃ = 39·2-47·8%.

Amorphous.

White; opaque; very soft.

Llano Co., Texas.

~Thalenite.~

H₂E₄Si₄O₁₅, with traces of Fe´´´ and Al. Yttr = 58·6-63·9%.

Monoclinic.

G = 4·23. H = 6¹⁄₂. Bright red and yellow,

Österby, Sweden.

~Thorianite.~

Mixed ThO₂ + UO₂, with E, Pb, Zr, Si, Fe, etc. ThO₂ = 72-79; Cer = 1-8%.

Rhombohedral; pseudocubic.

G = 8·0-9·7. H = 7. Jet black; bright resinous lustre.

Gem-gravels of Ceylon.

~Thorite.~

ThSiO₄, with H₂O, U, Fe, E, Ca, Al, etc. ThO₂ = 41·4-57·9; E₂O₃ = 0-6%.

Tetragonal; habit prismatic.

G = 4·4-4·8; H = 4¹⁄₂-5. Brown to black.

Various localities in Scandinavia.

_Thorogummite._

UO₃,3ThO₂,3SiO₂,6H₂O? An altered Mackintoshite (_q.v._)? ThO₂ = 41·4; E₂O₃ = 6·7%.

Usually massive; sometimes in crystals resembling Zircon.

G = 4·43-4·54. H = 4-4¹⁄₂. Dull brown; opaque.

Llano Co., Texas.

~Thortveitite.~

E₂O₃,2SiO₂, with Fe´´´, Al, Mn´´´ traces; E = chiefly Sc. Yttr = 54·5%.

Orthorhombic, in radial aggregates.

G = 3·571. H = 6-7. Greyish green; translucent.

Iveland, Sätersdalen, Norway.

~Titanite~ (Sphene, Grothite).

CaSiTiO₅, with Fe´´, Mn´´. TiO₂ = 34-45% (usually 41%).

Monoclinic; wedge-shaped.

G = 3·40-3·56. H = 5-5¹⁄₂. Yellow, green, or brown; pleochroism strong; lustre resinous.

Widely distributed in Europe and N. America.

Titanium Olivine.

(H₂,Fe´´,Mg)₂(Si,Ti)O₄; Mn and F in traces. TiO₂ = 3-12%.

Orthorhombic.

G = 3·25-3·27. H = 6¹⁄₂-7. Deep red to yellow; pleochroic.

Pfunders, Tyrol; Zermatt, Switzerland.

_Tritomite._

A fluo-borosilicate of E, Th, Ca, with Zr, Na, H₂O, etc. Cer = 44·2-59·2; Yttr = 0·4-4·6; ThO₂ + ZrO₂ = 0-10·6%.

Rhombohedral; in crystals resembling regular tetrahedra.

G = 4·15-4·25. H = 5¹⁄₂. Dark brown; transparent to opaque.

Langesund Fiord, Norway.

_Tscheffkinite._

Titano-silicate of E, Th, Fe, Ca, etc. Cer = 23-47; Yttr = 0-3·4; ThO₂ + ZrO₂ = 0-20; TiO₂ = 16-21%.

Massive, amorphous.

G = 4·26-4·55. H = 5-5¹⁄₂. Velvet black.

Ilmen Mountains; Nelson Co. and Bedford Co., Virginia, U.S.A.

_Tysonite._

Fluoride of E, with Th, H₂O, CO₂, etc. Cer = 69·2-70·6; ThO₂ = 0-31%.

Hexagonal; in thick prisms.

G = 6·12-6·14. H = 4¹⁄₂-5. Wax yellow; transparent to translucent.

Fahlun and Österby, Sweden; Pike’s Peak, Colorado.

_Uhligite._

Titanate of Zr, Ca, Al; Ca(Zr,Ti)O₃ + Al(Ti,Al)O₃? TiO₂ = 48; ZrO₂ = 22%.

Cubic; near to Perovskite (_q.v._).

H = 5-6. Black. Transparent in flakes.

Lake Magad, E. Africa.

~Uraninite.~

Oxides of U (60-75%), with PbO₂, ThO₂, ZrO₂, E₂O₃, Fe₂O₃, etc. Cer. = 0-2·7; Yttr = 0-10·2; ThO₂ = 1·6-11·1; ZrO₂ = 0-8·1%.

Cubic, usually massive; alters to amorphous pitchblende.

G = → 6·4 (massive); → 9·7 (crystalline). H = 5¹⁄₂. Black; transparent in splinters.

Norway; Bohemia; Saxony; Cornwall; Carolina, etc.

_Vietinghofite._

A hydrated ferruginous samarskite (_q.v._). E₂O₃ = 8·2; ZrO₂ = 1·0%.

Amorphous.

G = 5·53. H = 5¹⁄₂-6. Dull black; opaque.

Lake Baikal, Siberia.

Warwickite.

6MgO,FeO,2TiO₂,3B₂O₃? TiO₂ = 23·5%.

Orthorhombic; habit prismatic, elongated.

G = 3·35-3·36. H = 3-4. Dark brown to black; pleochroic. Double refraction strong, +ve.

Edenville, New York State.

_Weibyite._

Carbonate of E, with Ca, Sr, F, and H₂O; allied to Bastnäsite (_q.v._). Cer = 66·96%?

Orthorhombic; in pyramids resembling those of Zircon.

Crystals are small, and covered with a thin yellow crust; they are intergrown with Parisite (_q.v._)

Langesund Fiord, Norway.

~Wiikite.~

Titano-tantalo-silicate of Zr, Th, E, Fe, U, with Cb₂O₅, H₂O, etc. Cer = 2·5; Yttr = 7·6; Sc₂O₃ = 1·2; ThO₂ = 5·5; ZrO₂ + TiO₂ = 23·4%.

Perfectly amorphous.

G = 4·85. H = 6. Black; opaque; infusible.

Impilaks, Lake Ladoga, Finland.

_Wöhlerite._

Silicate and columbate of Ca, Zr, Na; Si₁₀Zr₃Cb₂O₄₂F₃Ca₁₀Na₅? ZrO₂ = 15·2-22·7%. Cer, traces.

Monoclinic; prismatic or tabular habit.

G = 3·41-3·44. H = = 5¹⁄₂-6. Light yellow; pleochroic.

Langesund Fiord.

~Xenotime.~

Phosphate of E, with ThO₂, SiO₂, Zr, etc. Cer = 0-11; Yttr = 54·1-64·7; ThO₂ = 1-5%.

Tetragonal; isomorphous with Zircon?

G = 4·45-4·56. H = 4-5. Brown to yellow; opaque.

Diamond sands of Brazil; Norway.

_Yttrialite_ (Green Gadolinite).

A weathered gadolinite (_q.v._)--E₂O₃,2SiO₂. Cer = 6·6-8·2; Yttr = 43·4-46·5; ThO₂ = 10·8-12·8%.

Amorphous, massive.

G = 4·6. H = 5¹⁄₂. Green to brown; translucent.

Bluffton, Llano Co., Texas.

~Yttrocerite.~

Ca₃E₂F₁₂, 1¹⁄₂H₂O. Cer = 9·3-18·2; Yttr = 8·1-29·4%.

Massive, granular.

G = 3·45. H = 4¹⁄₂. White to violet blue or brown.

Various localities in Scandinavia.

_Yttrocrasite._

(Ca,Pb)O,(Th,U)O₂,3E₂O₃,16TiO₂,6H₂O. Yttr = 25·7; Cer = 2·9; ThO₂ = 8·7; TiO₂ = 49·7%.

Orthorhombic; axial ratios unknown.

G = 4·80. H = 5¹⁄₂-6. Black; lustrous.

Burnet Co. Texas.

~Yttrofluorite.~

_n_CaF₂ + _m_YF₃ in isomorphous mixture? Yttr = 20-25; Cer = 1-2%.

Cubic.

G = 3·54-3·56. H = 4¹⁄₂. Closely resembles fluorspar, except in badness of cleavage.

Northern Norway.

_Yttrogarnet._

A variety of garnet with E and Zr. Yttr = 1-6·7; ZrO₂ = 0-3%.

Cubic (cf. Garnet).

Dark reddish brown (cf. Garnet).

Stockö, Norway; Schreiberhau, Germany.

_Yttrogummite._

UO₃, 3ThO₂, 3SiO₂, 6H₂O? E₂O₃ = 6·7; ThO₂ = 41·4%.

Tetragonal; angles near Zircon. Usually massive.

G = 4·43-4·54. H = 4-4¹⁄₂. Yellowish brown.

Llano Co., Texas.

_Yttrotantalite._

R´´R´´´₂(Cb,Ta)₄O₁₄ + 4H₂O; R´´ = Fe´´, Ca; R´´´ = E; Cer = 0-2·4; Yttr = 17·2-38·3%.

Orthorhombic; isomorphous with Samarskite (_q.v._).

G = 5·5-5·8. H = 5-6. Yellow to black.

Ytterby, Sweden; South Norway.

~Zircon.~

ZrSiO₄, with Fe, Th, etc., in traces. ZrO₂ = 61·0-70·0%.

Tetragonal; habit prismatic.

G = 4·68-4·70. varying considerably. H = 7¹⁄₂. Colour very variable.

Widely distributed as a rock mineral, in sands, etc.

_Zirkelite._

(Ca,Fe)(Zr,Ti,Th)₂O₅, with E, U, Mg, etc. ZrO₂ = 48·9-52·9; ThO₂ = 0-7·3; TiO₂ = 14-15; E₂O₃ = 0-3%.

Cubic; in twinned octahedra.

G = 4·7. H = 5. Black; transparent in thin flakes.

Jacupiranga, São Paulo, Brazil.