Part 13

The Brown Iron Ores of Eastern Texas, by E. B. Eckel. U. S. Geol. Survey Bull. 902 (1938).

*The Rustler Springs Sulphur Deposits as a Source of Fertilizer, by G. L. Evans. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 1 (1946).

Origin of the Gulf Coast Salt-Dome Sulphur Deposits, by Herbert W. Feely and J. Lawrence Kulp. Bull. Amer. Assoc. Petrol. Geol., vol. 41, pp. 1802-1853 (1957).

*Pegmatites of the Van Horn Mountains, Texas, by P. T. Flawn. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 9 (1951).

*The Hazel Copper-Silver Mine, Culberson County, Texas, by P. T. Flawn. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 16 (1952).

*Basement Rocks of Texas and Southeast New Mexico, by P. T. Flawn. Univ. Texas Pub. 5605 (1956).

*Texas Miners Boost Talc Output, by P. T. Flawn. Univ. Texas, Bureau Econ. Geol. Rept. Inves. No. 35 (1958).

*Geology and Mineral Deposits of Pre-Cambrian Rocks of the Van Horn Area, Texas, by P. B. King and P. T. Flawn. Univ. Texas Pub. 5301 (1953).

*Igneous Rocks of the Balcones Fault Region of Texas, by J. T. Lonsdale. Univ. Texas Bull. 2744 (1927).

Mineral Resources of the Llano-Burnet Region, Texas, with an Account of the Pre-Cambrian Geology, by Sidney Paige. U. S. Geol. Survey Bull. 450 (1911).

*Mineral Resources of the Texas Coastal Plain (Preliminary Report), by J. M. Perkins and J. T. Lonsdale. Univ. Texas, Bureau Econ. Geol. Mineral Resource Circ. 38 (1955).

Geology and Ore Deposits of the Shafter Mining District, Presidio County, Texas, by C. P. Ross. U. S. Geol. Survey Bull. 928-B (1943).

*The Geology of Texas, Vol. II, Structural and Economic Geology, by E. H. Sellards, C. L. Baker, and others. Univ. Texas Bull. 3401 (1935).

*Texas Mineral Resources, by E. H. Sellards and others. Univ. Texas Pub. 4301 (1946).

*Geological Resources of the Trinity River Tributary Area in Texas and Oklahoma, by H. B. Stenzel, A. E. Weissenborn, and others. Univ. Texas Pub. 4824 (1948).

Uranium at Palangana Salt Dome, Duval County, Texas, by A. D. Weeks and D. H. Eargle. _In_ U. S. Geol. Survey Prof. Paper 400-B (1960).

Geology of the Quicksilver Deposits of the Terlingua District, Texas, by R. G. Yates and G. A. Thompson. U. S. Geol. Survey Prof. Paper 312 (1959).

GLOSSARY

Amorphous—without crystalline structure and therefore without regular form.

Balcones fault zone—a system of faults extending from north of Waco in McLennan County, through Travis and Bexar counties, to near Del Rio in Val Verde County (_see_ p. 42).

Boulder—a large rock or mineral fragment that has a diameter greater than 256 millimeters (about 10 inches).

Breccia—a rock made up of sharp-cornered, cemented fragments with diameters greater than 2 millimeters (about ⁸/₁₀₀ of an inch).

Cambrian—the earliest period of the Paleozoic Era (_see_ p. 3).

Cenozoic—the present era, one of the great divisions of geologic time (_see_ p. 3). This era began about 63 million years ago.

Clastic—made up of broken fragments of rocks or minerals.

Cleavage—occurs when minerals split along smooth flat surfaces that are parallel to possible crystal faces. These planes as well as crystal faces are controlled by the crystal lattice or atomic structures of the minerals.

Cleavage fragment—a mineral specimen that has been broken along its planes of cleavage.

Cobble—a rock or mineral fragment that has a diameter between 64 and 256 millimeters (about 2½ and 10 inches).

Conchoidal—a curved fracture surface shaped like the inside of a shell or spoon.

Conglomerate—a rock composed of cemented, rounded rock or mineral fragments, most of which are of gravel size.

Cretaceous—the third and latest period of the Mesozoic Era (_see_ p. 3).

Cryptocrystalline—made up of tiny crystalline particles that are too small to be distinguished even under high magnification.

Crystalline—having a definite, orderly internal structure.

Cube—a solid that has six equal, square sides.

Dodecahedron—a solid that has twelve plane, four-sided faces.

Element—a basic building block of all matter, which cannot be separated into different substances by ordinary chemical means.

Eocene—the second epoch of the Tertiary Period (_see_ p. 3).

Epoch—a unit of geologic time that is a subdivision of a period.

Era—a major division of geologic time, which consists of several periods.

Extrusive rocks—igneous rocks formed from magma that was extruded on the earth’s surface.

Fault—a break in the rocks or strata of the earth’s crust along which movement or slippage has taken place.

Fluid—a substance made up of particles that can move freely about; it can be a liquid or a gas.

Formation—rocks or strata that are recognized and mapped as a unit.

Fracture—the kind of surface obtained if a mineral is broken in a different direction from that of the cleavage or parting. Commonly, fracture surfaces are rough, uneven, or curved, whereas cleavage surfaces are smooth.

Geologic map (areal)—shows the extent and distribution of formations exposed at the earth’s surface.

Granular—the texture of a rock or mineral that is made up of visible grains. If all the grains are about the same size, the term _equigranular_ is used.

Granule—a rock or mineral fragment that has a diameter of from 2 to 4 millimeters (about ⁸/₁₀₀ to ¹⁵/₁₀₀ of an inch).

Gravel—uncemented rock or mineral fragments that have diameters greater than 2 millimeters (about ⁸/₁₀₀ of an inch).

Gulf Coastal Plain—an area that extends, in Texas, from the Gulf of Mexico to the Balcones fault zone and in which Quaternary, Tertiary, and Upper Cretaceous strata crop out at the surface (_see_ p. 42).

High Plains—an area in northwest Texas extending from the Pecos River valley north to the Oklahoma-Texas boundary (_see_ p. 42).

Igneous rocks—rocks formed by the cooling and hardening of hot, molten rock material.

Intrusive rocks—igneous rocks that have formed below the surface of the earth.

Lava—molten rock material that has poured out onto the earth’s surface from volcanoes; also the rock that is formed after the molten material has cooled and hardened.

Llano uplift—an area in central Texas where Precambrian and early Paleozoic rocks occur at the earth’s surface (_see_ p. 42).

Magma—hot, molten rock material from which igneous rocks form.

Massive—in a mass, without a regular or complete form.

Mesozoic—an era, one of the great divisions of geologic time (_see_ p. 3). This era began about 230 million years ago and lasted until about 63 million years ago.

Metamorphic rock—rock formed from igneous or sedimentary rocks that are altered by heat, pressure, and fluids below the earth’s surface.

Miocene—the fourth epoch of the Tertiary Period (_see_ p. 3).

Mississippian—the fifth period of the Paleozoic Era (_see_ p. 3).

Nodule—a small, rounded mass or lump.

Octahedron—a solid that has eight triangular faces.

Opaque—no light can pass through.

Ordovician—the second period of the Paleozoic Era (_see_ p. 3).

Paleozoic—an era, one of the great divisions of geologic time (_see_ p. 3). This era began at the end of Precambrian time and lasted until about 230 million years ago.

Parting—occurs when a mineral breaks along a flat surface that is not a true cleavage plane.

Pebble—a rock or mineral fragment that has a diameter between 4 and 64 millimeters (about ¹⁵/₁₀₀ and 2½ inches).

Pennsylvanian—the sixth period of the Paleozoic Era (_see_ p. 3).

Period—a unit of geologic time, a subdivision of an era.

Permian—the last period of the Paleozoic Era (_see_ p. 3).

Physiographic outline map—shows location of natural regions (p. 42).

Playa lake—a temporary shallow lake in a nearly level, closed basin, which has no drainage outlet.

Pleistocene—the first epoch of the Quaternary Period (_see_ p. 3).

Pliocene—the last epoch of the Tertiary Period (_see_ p. 3).

Precambrian—comprises the Early and the Late Precambrian Eras, the earliest great divisions of geologic time. Rocks that formed more than 600 million years ago are known as Precambrian rocks.

Pyritohedron—a solid that has twelve 5-sided faces.

Quaternary—the present period of geologic time; the second period of the Cenozoic Era (_see_ p. 3).

Recent—the present epoch of geologic time; the second epoch of the Quaternary Period (_see_ p. 3).

Sectile—describes material, such as soap, that can be cut smoothly with a knife.

Sediments—material deposited by water, wind, or ice on the earth’s surface.

Sedimentary rocks—rocks made up of sediments.

Series—a subdivision of a system that includes all rocks formed during an epoch.

Specific gravity—the ratio of the weight of a substance to the weight of an equal volume of water.

Streak—the color of the powder of a mineral.

System—all rocks formed during a period.

Tertiary—the first period of the Cenozoic Era (_see_ p. 3).

Translucent—light will pass through, but objects cannot be seen.

Transparent—light will pass through, and objects can be seen.

Trans-Pecos—area of Texas located west of the Pecos River (_see_ p. 42).

Volcanic rocks—igneous rocks that have formed on the earth’s surface; extrusive rocks.

Index

A acid: 18, 22 acid tests (_see also_ chemical tests): 18 actinolite: 82 schist: 87 agate: 21, 83 agatized wood: 20, 84 age, earth’s crust: 2 alabaster: 65 albite: 55 alkali lakes: 66, 83 Allamoore: 87, 93 alloys: 52 almandite: 58 Alpine: 57, 78, 82, 90 Altuda Mountain: 57, 90 amalgam: 51 amazonstone: 56 amethyst: 37, 82 Amethyst Hill: 82 amorphous minerals, definition of: 15 amphibole asbestos: 29, 33, 34, 44 Anderson County: 70 Andrews County: 83 Angelina County: 52 anhydrite: 28, 29, 30, 35, 36, 43, 65, 66, 91 anthophyllite: 93 antigorite: 87 Apache Mountains: 65 apatite: 72 Archer County: 52 argentite: 26, 27, 89, 90 argentiferous galena: 57, 90 Armstrong County: 79 asbestos: 43 amphibole: 29, 33, 34, 44 chrysotile: 44, 87 ash, volcanic: 41, 97 augite: 45 Austin: 46, 62 autunite: 97 azurite: 35, 52, 53, 54

B Babyhead: 72 Balcones fault zone: 10, 42, 45, 88 Bandera County: 45 Baringer Hill pegmatite: 80 barite: 15, 28, 31, 32, 35, 36, 38, 44, 48 barium: 45 Barrilla Mountains: 85 Baylor County: 45, 52, 98 basal cleavage: 76, 93, 94 basalt: 40, 41, 45 basement: 2, 9 Bastrop County: 64 Bell County: 69 bentonite: 51, 52 beryllium: 80 Big Bend area: 9, 42, 51, 75, 77 Big Branch Gneiss: 59 biotite: 32, 33, 34, 76 Bird mine: 90 Blanco County: 44, 58, 59, 61, 70, 83, 87, 94 black mica (_see_ biotite) blast furnace: 70, 71 blast sand: 86 bleaching clay: 51 blue copper: 53 Boerne: 18 Boling salt dome: 91 books about rocks and minerals: 24, 39, 100 brass: 52 braunite: 26, 27, 73 Brazoria County: 91 Brazos County: 98 Brazos River, Double Mountain Fork and Salt Fork of: 43 breccia: 12, 41, 81 Brewster County: 45, 46, 47, 49, 50, 57, 65, 70, 76, 77, 78, 82, 84, 85, 90 brimstone: 90 bronze: 52 Brooks County: 64 Brown, Thomas E.: vii Brown County: 45, 49 brown iron ore (_see also_ limonite): 70 Bryan Mound salt dome: 91 building sand: 85 Burnet: 56, 80, 97 Burnet County: 18, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 70, 76, 79, 80, 81, 82, 83, 97

C calcareous sinter and tufa: 46 calcite: 7, 14, 18, 19, 20, 21, 28, 30, 31, 32, 34, 35, 36, 38, 45, 46, 49, 50, 51, 54, 56, 64, 68, 75, 86, 87, 88, 91 dog-tooth spar: 46, 47 Caldwell County: 88 caliche: 46, 47 Cambrian: 2, 3, 55, 58, 69, 86 Cameron County: 66 Capitan reef limestone: 1 Capitol building, Texas State: 62 cap-rock: 91, 92 carats: 60 carbon: 62, 63 carbonized wood: 20 carnotite: 30, 95, 97 Carrizo Mountains: 67, 83, 95 Casey, Miss Josephine: vii Cass County: 70 cassiterite: 27, 32, 47 Castile Gypsum: 91 Catahoula strata: 78, 86, 97 cave deposits: 18 caves: 18, 19, 49 Caverns of Sonora: 19 Cedar Lake: 83 Cedar Park: 70 celestite: 20, 28, 30, 35, 38, 48 cementing materials: 12, 46, 67, 70, 86 cerargyrite: 28, 29, 34, 37, 89, 90 cerium: 80 chalcedony (_see also_ agate): 16, 21, 45, 78, 81, 83, 86 chalcocite: 21, 26, 27, 52, 54, 73, 89 chalcopyrite: 26, 52, 53, 54, 60 chalk: 40, _69_ chemical elements: 7 chemical sediments: 12 chemical tests: 18, 43, 46, 47, 49, 52, 53, 54, 64, 68, 75 Cherokee County: 70 chert: 19, 40, 81, 84 chessylite: 53 china clay: 51 Chinati Mountains: 45, 57, 62, 85 Chisos Mountains: 45, 62, 85 chlorite: 93 schist: 87 chrysotile: 44, 87, 88 asbestos: 44, 87 cinnabar: 36, 49 clastic rocks: 12 clay: 40, 45, 49, 51, 70, 86, 88, 91 bentonite: 45, 51, 52 bleaching clay: 51 china clay: 51 kaolin: 51 clay minerals: 51 Clay County: 52 Clear Creek area: 63 cleavage: 17 basal: 76, 93, 94 cubic: 17, 57, 65 octahedral: 56, 57 pyramidal: 74 rhombohedral: 46, 54 Clemens salt dome: 91 Coal Creek serpentine: 87, 88 Coke County: 20, 49 Coleman County: 86 color of minerals: 16 columns: 18 Comal County; 45, 69 Comanche County: 49 common opal: 78 composition of minerals: 99 concretions: 19 conglomerate: 11, 12, 41, 55, 81 gneiss: 59 contact metamorphism: 13 copper: 52, 59, 90 blue copper: 53 glance: 52 green copper carbonate: 53 minerals: 52 pyrites: 53 yellow copper ore: 53 coquina: 41, 69 Crane County: 66 Cretaceous: 2, 3, 20, 21, 45, 46, 49, 51, 55, 57, 60, 65, 68, 69, 70, 74, 75, 84, 86, 88 cryptocrystalline quartz: 81, 84 crystal, definition of: 14 crystals, twinned: 46, 63 crystalline minerals, definition of: 14 Crosby County: 79 crust, earth’s: 2 cubic cleavage: 17, 57, 65 Culberson County: 1, 45, 52, 53, 58, 59, 60, 65, 75, 79, 83, 90, 91, 95

D Daingerfield: 70 Dallas: 88 Damon Mound salt dome: 91 daughter elements: 95, 96 Davis Mountains: 45, 85, 98 Delaware Mountains: 65 diamond: 62 diatomaceous earth: 78 diatomite: 40, 78 Dickens County: 79, 98 Dietrich, John W.: vii dikes: 72, 79 dog-tooth spar: 46, 47 dolomite: 29, 30, 32, 36, 38, 40, 43, 54, 68, 75, 87, 88 dolomitic limestone: 68 Double Mountain Fork of the Brazos River: 43 double refraction: 46 dravite: 95 Duval County: 78, 83, 91, 97 dynamic metamorphism: 14

E Eagle Flat: 93 Eagle Mountains: 56, 57, 90, 95 earth’s crust: 2 east Texas: 70 Ector County: 79 Edwards Limestone: 68, 69, 84 effervescence in acid: 18 El Capitan Peak: 1 elements: 7, 8, 95, 96 Ellenburger strata: 55, 84 El Paso: 48, 58, 85, 88 El Paso County: 48, 58, 62 epoch: 2 era: 2 erosion: 11 extrusive igneous rocks, definition of: 9

F Fairland: 54 Falfurrias: 64 Fannett salt dome: 91 Fayette County: 52, 64, 84, 98 feldspar: 8, 29, 30, 31, 33, 34, 35, 37, 45, 51, 55, 59, 61, 72, 79, 80, 85, 86 albite: 55 amazonstone: 56 microline: 55, 56, 61 orthoclase: 55, 61 fibrous gypsum: 64, 65 filtering sand: 86 Fisher County: 20, 49, 58, 65 Flawn, Peter T.: vii flint: 84 flowstone: 18 flow structure: 85 fluorite: 29, 32, 34, 35, 37, 38, 56, 72 Foard County: 52, 58 foliation: 87 fool’s gold: 53, 80 formation: 6 Fort Bend County: 91 Fort Worth: 88 fracture of minerals: 17 fragmental rocks: 12 Franklin Mountains: 48, 58, 62, 85 Frasch method of sulfur mining: 91, 92 Fredonia: 67 Freer: 78, 83 furnace (_see_ blast furnace; open-hearth furnace)

G gabbro: 87 gneiss: 59 Gaines County: 83 galena: 17, 26, 57, 89, 90 argentiferous: 57, 90 Galveston County: 91 Gamble prospect: 67 gamma rays: 96 garnet: 31, 33, 34, 37, 58, 85, 87 Garza County: 97 Geiger counter: 96 gemstones: 56, 58, 77, 82, 94, 95 geode: 19, 46, 49, 82 geologic map: 4, 5 geologic time scale: 2, 3 geologists: 2 geology: 2 Gillespie County: 44, 45, 55, 58, 59, 60, 61, 65, 76, 80, 82, 83, 87, 88, 94 glass, natural: 9, 77, 85, 97 glass sand: 85-86 glauconite: 70, 73 glossary: 102-103 gneiss: 13, 41, 55, 56, 59, 67, 72, 73, 74, 76, 81, 87, 93, 97 conglomerate: 59 gabbro: 59 granite: 59 hornblende: 59 mica: 59 goethite: 70 gold: 26, 51, 59, 80, 90 fool’s: 53, 80 Gonzales County: 52, 84, 97 Grand Saline salt dome: 66 granite: 2, 8, 9, 13, 41, 48, 55, 56, 59, 61, 72, 76, 79, 81, 85, 87, 94, 95 gneiss: 59 opaline: 72 Granite Mountain: 62 Granite Shoals Lake: 56 granules: 85 graphite: 26, 27, 62, 75 schist: 63, 87 gravel: 12, 41, 91 green copper carbonate: 53 greensands: 70 Grit: 94 grossularite: 58 group: 6 Guadalupe Mountains, Peak: 1 Gulf Coast: 91 Gulf Coastal Plain: 20, 42, 43, 46, 51, 52, 58, 60, 65, 66, 78, 83, 84, 86, 87, 92, 97, 98 Gulf salt dome: 91 Gyp Hill salt dome: 64 gypsite: 65 gypsum: 28, 29, 30, 32, 36, 37, 43, 63, 70, 85, 91 alabaster: 65 fibrous gypsum: 64, 65 rock gypsum: 40, 65 rosettes: 63, 64 satin spar: 64 selenite: 63, 64, 76

H halite: 28, 32, 34, 35, 36, 38, 40, 43, 65, 91 hand lens: 22 Hardeman County: 52, 58, 64, 65 hardness of minerals: 16, 99 Harris, Bill M.: vii Harris, John S.: vii Harris County: 65, 66 Hartley County: 79 Hays County: 45 Hazel Formation: 52 Hazel mine: 52, 53, 90 Heath mine: 60 hematite: 26, 27, 36, 66, 75, 84, 86 specular: 67 Henderson County: 70 High Island salt dome: 91 High Plains: 42, 46, 51, 65, 66, 78, 79, 83, 87, 97, 98 Hockley salt dome: 65, 66 hollandite: 26, 27, 28, 73, 74 Honey Creek area: 87 hornblende: 8, 59, 61 gneiss: 59 schist: 87 horn silver: 90 Hoskins Mound salt dome: 91 Houston: 70 Howard County: 45, 60 Hudspeth County: 45, 52, 53, 55, 56, 57, 58, 59, 60, 62, 65, 66, 67, 75, 79, 82, 83, 90, 93, 95 Humphreys, Alan: vii Hutchinson County: 66 hyalite: 78 hydrochloric acid (_see also_ chemical tests): 18, 22

I identification charts: 24 igneous rocks, definition of: 9 intrusive igneous rocks, definition of: 9 Irion County: 60 iron: 59, 66, 67, 69, 70, 72, 73 Iron Mountain: 73

J Jackson strata: 97 jasper: 81, 84 Jasper County: 52 Jeff Davis County: 45, 51, 74, 78, 85 Jefferson County: 91 Johnson County: 69

K kaolin: 51 kaolinite: 51 karats: 60 Karnes County: 97, 98 Katemcy: 94 Kendall County: 18 Kenedy County: 66 Kent County: 98 kidney ore: 67 King, Elbert A., Jr.: vii King County: 52 Kinney County: 45 Kleberg County: 66 Knox County: 52

L labeling rock and mineral specimens: 23 labradorite: 45 Lake Buchanan: 80, 83 Lamb County: 79 Lampasas County: 20, 48, 49, 88 lava: 9 lead: 57, 90 Leakey: 51 Lee County: 64, 84 lens: 22 Liberty County: 91 lime: 69 limestone: 12, 13, 18, 19, 40, 43, 45, 46, 49, 54, 55, 56, 57, 58, 60,68, 74, 75, 76, 84, 88, 90, 91 chalk: 69 dolomitic: 68 lithographic: 69 öolitic: 69 pulverulent: 41, 69 limonite: 19, 27, 28, 30, 32, 70, 75, 81, 86 lithographic limestone: 69 Live Oak County: 45, 97 llanite: 41, 71, 81 Llano: 60, 63, 72, 73, 95 Llano County: 44, 45, 55, 56, 58, 59, 60, 61, 63, 70, 71, 72, 73, 76, 78, 80, 83, 87, 88, 94, 95 Llano uplift: 10, 18, 42, 44, 52, 55, 56, 58, 59, 60, 61, 62, 63, 67, 70, 72, 76, 77, 79, 80, 82, 83, 84, 85, 86, 87, 88, 93, 94, 95 Lone Grove: 63 Lone Star: 70 Longhorn Cavern: 18 Long Point salt dome: 91 Lonsdale, John T.: vii luster of minerals: 16 Lytton Springs oil field: 88

M Macon, James W.: vii magma: 9 magnesium, source of: 55 magnetite: 28, 67, 70, 72, 85, 87, 93 malachite: 34, 52, 53, 54 Malone Mountains: 65 manganese: 73, 75 map— geologic: 4-5 physiographic outline: 42 Marathon area: 42, 84, 88 marble: 13, 14, 40, 46, 54, 75 Marble Falls: 62 Marion County: 70 martite: 67 Mason: 74 Mason County: 48, 55, 58, 59, 60, 61, 67, 72, 73, 74, 76, 80, 83, 94 masses, crystalline, definition of: 14 Matagorda County: 91 Mayfield prospect: 74 McCulloch County: 88 Medina County: 45 Menard County: 65 mercury: 8, 49, 50, 51 metamorphic rocks, definition of: 12 metamorphism, definition of: 13, 14 mica (_see also_ biotite; muscovite): 8, 60, 61, 63, 64, 72, 76, 79, 80, 85, 87 mica gneiss and/or schist: 59, 76, 87 Mica Mine area: 58, 76, 77, 79 microcline: 55, 56, 61 milky quartz: 82 Mills County: 49 mineral identification charts: 24 mineralogists: 2 minerals, definition of: 7, 14, 15 Mississippian: 3, 55, 69, 88 Mitchell County: 66 Mohs scale of hardness: 16, 17 molybdenite: 63 montmorillonite: 51 Morris County: 70 moss agate: 84 Moss Bluff salt dome: 91 muriatic acid: 22 muscovite: 31, 32, 34, 37, 38, 76

N Nacogdoches County: 70 Nash salt dome: 91 native elements: 8 native mercury: 8 native silver: 26, 89 nodule: 19, 44, 49 Nolan County: 20, 49, 63, 64, 65 north-central Texas: 43, 51, 52, 69, 70, 86, 88

O Oakville strata: 97 obsidian: 40, 77 occurrence of minerals: 14 ocher, red: 67 octahedral cleavage: 56, 57 oil shale: 88 olivine: 88 onyx: 84 öolitic limestone: 69 opal: 21, 29, 30, 31, 35, 37, 38, 78, 86 opaline granite: 72 opalized wood: 20, 78, 84 open-hearth furnace: 70, 72 Orchard salt dome: 91 Ordovician: 3, 55, 69, 84 orthoclase: 55, 61

P Packsaddle Mountain: 87 Packsaddle Schist: 87 Palangana salt dome: 91, 97 paleontologists: 2 parting of minerals: 17 Pavitte prospect: 53 Pecos County: 9 Pecos River: 65, 74, 75 pegmatite: 41, 55, 56, 58, 76, 77, 79, 81, 94, 95 Baringer Hill: 80 Pennsylvanian: 3, 45, 51, 55, 69, 70, 86, 88 peridotite: 88 period: 2 Permian: 1, 3, 20, 21, 43, 45, 49, 52, 55, 64, 65, 69, 86, 90 Permian basin: 42, 43, 65, 66 petrified wood: 20, 52, 78, 84 petrologists: 2 phenocrysts: 85 physiographic outline map: 42 pitchblende: 28, 95, 97 placer deposits: 60 Plata Verde mine: 90 Polk County: 98 porphyritic rocks: 45, 85 portland cement: 51, 69, 88 Precambrian: 2, 3, 44, 45, 48, 52, 53, 56, 58, 59, 60, 61, 63, 67, 72, 74, 75, 76, 79, 82, 85, 87, 93, 94, 95, 97 precious opal: 78 Presidio County: 45, 49, 57, 60, 62, 67, 77, 78, 84, 85, 90, 97 Presidio mine: 60, 90 properties of minerals: 14 pseudomorphs: 70, 87 pulverulent limestone: 41, 69 pumicite: 97, 98 pyramidal cleavage: 74 pyrite: 19, 26, 60, 70, 80, 87 pyrolusite: 27, 73, 74 pyroxene: 45

Q quartz: 8, 20, 29, 30, 31, 33, 36, 37, 38, 48, 51, 54, 56, 59, 60, 61, 68, 72, 78, 79, 80,81, 84, 85, 86, 94 agate: 21, 83, 84 amethyst: 37, 82 chalcedony: 16, 21, 45, 78, 81, 83, 86 chert: 19, 40, 81, 84 cryptocrystalline: 81, 84 jasper: 81, 84 milky: 82 onyx: 84 rock crystal: 82 rose: 82, 83 smoky: 82, 83 quartzite: 41, 74, 84, 86 Quaternary: 2, 3, 51, 79, 98 quicksilver (_see also_ mercury): 50 Quitman Mountains: 57, 58, 60, 62, 67, 82, 90

R radioactivity: 95, 96 Real County: 49, 51 Recent: 2, 3 “red beds”: 52 red ocher: 67 reef limestone: 1, 12 Reeves County: 65, 85, 91 reference books: 24, 39, 100 refraction, double: 46 rhombohedral cleavage: 46, 54 rhyolite: 40, 85 porphyry: 41, 85 Rio Grande: 83, 84, 97 rock— crystal: 82 gypsum: 40, 65 identification charts: 39 salt: 40, 65 units: 2 rocks, definition of: 8 Rodda, Peter U.: vii rose quartz: 82, 83 rosettes: 63, 64 Rustler Springs area: 91 rutile: 82