PART I—SECTION A

THE CHARACTERS OF GEM-STONES

II. CRYSTALLINE FORM 6

III. REFLECTION, REFRACTION, AND DISPERSION 14

IV. MEASUREMENT OF REFRACTIVE INDICES 21

V. LUSTRE AND SHEEN 37

VI. DOUBLE REFRACTION 40

VII. ABSORPTION EFFECTS: COLOUR, DICHROISM,ETC. 53

VIII. SPECIFIC GRAVITY 63

IX. HARDNESS AND CLEAVABILITY 78

X. ELECTRICAL CHARACTERS 82