DIAMOND—BOART
- Crystalline System: Isometric.
- Forms: Octahedron, dodecahedron. Crystals frequently twinned.
- Hardness: 10. Scratches every other stone.
- Lustre: Adamantine. Transparent and when dark, translucent.
- Refraction: Single.
- Chemical Composition: Pure Carbon.
- Chemical Symbol: C.
- Specific Gravity: 3.50-3.55.
- Properties: Exhibits positive electricity when rubbed, but is itself a non-conductor of electricity. When intensely heated it burns, yielding Carbonic Anhydride. When heated so as to exclude chemical combination it dilates and forms into a black concretion. It displays phosphorescence under Radium, when submitted to strong sunlight and, when put in a vacuum tube, to a high tension electric current. Dr. G. F. Herbert Smith found that "some diamonds fluoresce in sunlight, turning milky, and a few emit light when rubbed." Dr. Kunz proved that diamonds phosphoresce when exposed to the rays of Radium, Polonium, or Actinium, even when glass is interposed. These phenomena formed special object of experiment with the late Sir William Crooks, who showed that exposed to high tension electric currents in greatly rarified atmosphere, the diamond phosphoresced with an intense green light. Prismatic colours are radiated by this gem.
- In the Zodiac: The Diamond is under the Heavenly Aries, Leo and Libra.
- Where found: India, Borneo, Brazil, South Africa, Siberia, Australia, United States of America.
GARNET
ALMANDINE, PYROPE, HESSONITE, (GARNET HYACINTH), UVAROVITE
- Crystalline Form: Isometric.
- Hardness: 6.5-7.5.
- Lustre: Vitreous.
- Refraction: Single.
- Chemical Composition: Silica Alumina, Red Iron Oxide, Lime Magnesia, Manganese, Protoxide.
- Chemical Symbol: Dr. Smith has the following formulae:
- Hessonite Ca3 Al2(SiO4)3.
- Pyrope Mg3 Al2(SiO4)3.
- Almandine Fe3Al2(SiO4O)3.
- Andradite Ca3Fe2(SiO4O)3.
- Specific Gravity: 3.4-4.3.
- Properties: Exhibits positive electricity by friction. With the exception of Uvarovite, all varieties of Garnets fuse before the blowpipe flame. The stone generally does not contain water.
- In the Zodiac: The Almandine is under the Heavenly Sagittarius; the Pyrope, Aquarius; Hessonite, Virgo; Uvarovite, Aquarius.
- Where found: Generally all over the world.
OPAL
- Crystalline System: None.
- Form: Amorphous.
- Hardness: 5.5-6.5.
- Lustre: Waxy to subvitreous.
- Refraction: Single.
- Chemical Composition: Silica 91.32. Water 8.68.
- Chemical Symbol: SiO2, n=SiO2nH2O.
- Specific Gravity: 1.9-2.3.
- Properties: No electrical properties. Opal exhibits characteristic colour reflections known as Opalescence. It is susceptible to heat and weather changes, exhibiting greater brilliancy on hot than on cold days. The opal has never yet been successfully imitated, and certain peculiar properties yet remain to be investigated. Professor Frank Rutley F. G. S., emphasises the fact that "the nature of the Silica (Hydrous Silica) is not yet definitely determined." It is infusible before the blowpipe, but turns opaque.
- In the Zodiac: The Opal is under the Heavenly Leo, Libra and Aquarius. Leo favours red and fire opal; Libra, light translucent, pure colours, etc.; Aquarius, dark, black Opal, etc.
- Where found: Hungary, Honduras, Mexico, United States. The finest opal is now found in Australia, principally at Lightning Ridge, White Cliffs, Stuart’s Range, Charleville, etc. (Mr. Conrad H. Sayce gives (“Australasian,” March issue, 1920) an analysis of Stuart’s Range opal, bearing earth which contains about 35 per cent each of Alumina and Sulphur trioxide. He opines that this may account for the harmful effect it has on the men’s eyes and lungs.)
PEARL
- Hardness: 3.5-4.
- Lustre: Translucent.
- Chemical Composition: Carbonate of Lime and Organic matter.
- Specific Gravity: 2.65-2.89.
- Properties: Affected by acids. Benefitted by some skins, adversely affected by others. Destroyed by fire.
- Where found: Persian Gulf, Ceylon, Red Sea, South America, New Guinea, Thursday Island, Australia, etc.
- In the Zodiac: Pearls are under the Heavenly Cancer.
PERIDOT