Quartz.

Hardness and specific gravity are two of the major characteristics of gemstones.

Hardness of a gemstone is its resistance to scratching and may be described relative to a standard scale of 10 minerals known as the Mohs scale. F. Mohs, an Austrian mineralogist, developed this scale in 1822.

Specific gravity is the number of times heavier a gemstone of any volume is than an equal volume of water; in other words, it is the ratio of the density of the gemstone to the density of water.

The 16 mineral gemstone groups listed below are highly prized for their beauty, durability, and rarity:

Gachala Emerald.	Beryl (hardness: 7.5-8 Mohs) Beryllium aluminum silicate Specific gravity: 2.63-2.91 Emerald: Intense green or bluish green Aquamarine: Greenish blue or light blue Morganite: Pink, purple pink, or peach Heliodore: Golden yellow to golden green Red beryl: Raspberry red Goshenite: Colorless, greenish yellow, yellow green, brownish
Cat's Eye.	Chrysoberyl (hardness: 8.5 Mohs) Beryllium aluminum oxide Specific gravity: 3.68-3.78 Chrysoberyl: transparent yellowish green to greenish yellow and pale brown Alexandrite: red in incandescent light and green in daylight Cat's eye: usually yellowish or greenish
Star Ruby.	Corundum (hardness: 9 Mohs) Aluminum oxide Specific gravity: 3.96-4.05 Ruby: Intense red Sapphire: Blue
Hope Diamond.	Diamond (hardness: 10 Mohs) Carbon Specific gravity: 3.51 Colorless to faint yellowish tinge, also variable
Orthoclase.	Feldspar (hardness: 6-6.5 Mohs) Two distinctly different alkali alumino silicates: the Plagioclase and the Alkali Feldspar Series Specific gravity: 2.55-2.76 Plagioclase Series- Labradorite: Colorful, iridescent, also transparent stones in yellow, orange, red, and green Sunstone: Gold spangles from inclusions of hematite Peristerite: Blue white iridescence Alkali Feldspar Group- Orthoclase: Pale yellow, flesh red Amazonite: Yellow green to greenish blue Moonstone: Colorless; also white to yellowish, and reddish to bluish gray
Grossular.	Garnet (hardness: 6.5-7.5 Mohs) A group of silicate minerals Specific gravity: 3.5-4.3 Almandine: Orangy red to purplish red Almandine-spessartine: Reddish orange Andradite: Yellowish green to orangy yellow to black Demantoid: Green to yellow green andradite Topazolite: Yellow to orangy yellow Grossular: Colorless; also orange, pink, yellow, and brown Tsavorite: Green to yellowish green Hessonite: Yellow orange to red Pyrope: Colorless; also pink to red Chrome pyrope: Orange red Pyrope-Almadine: Reddish orange to red purple Pyrope-Spessartine: Greenish yellow to purple Malaia: Yellowish to reddish orange to brown Color-change garnet: Blue green in daylight to purple red in incandescent light Rhodolite: Purplish red to red purple Spessartine: Yellowish orange Uvarovite: Emerald green
Jade Pendant.	Jade (hardness: 6 Mohs) Nephrite Calcium magnesium silicate Specific gravity: 2.9-3.1 White, deep green, creamy brown Jadeite Sodium aluminum silicate Specific gravity: 3.1-3.5 White, leafy and blue green, emerald green, lavender, dark blue green and greenish black, deep emerald-green
Lapis lazuli.	Lapis lazuli (hardness: 5-5.5 Mohs) A rock composed mainly of the mineral lazurite with variable amounts of pyrite (brassy flecks) and white calcite Specific gravity: 2.7-2.9 Deep blue, azure blue, greenish blue (bluish color with flecks of white and gold)
Opal.	Opal (hardness: 5.5-6.5 Mohs) Hydrated silica Specific gravity: 1.98-2.25 White opal: Opaque, porcelain-like white material; colors resemble flashes or speckles Black opal: Flashes and speckles appear against black background Water opal: A transparent, colorless opal is the background for brilliant flashes of color Fire opal: Reddish or orange opal
Peridot.	Peridot [Olivine] (hardness: 7 Mohs) Magnesium iron silicate Specific gravity: 3.22-3.45 Olive to lime green
Amethyst.	Quartz (hardness: 7 Mohs) Silicon dioxide or silica Specific gravity: 2.65 Coarsely crystalline varieties of silica- Rock crystal: Colorless Amethyst: Purple Citrine: Yellow to amber Morion: Black Smoky quartz or cairngorm: smoky gray to brown Rose quartz: Translucent pink Green quartz or praziolite: Green Cryptocrystalline varieties of silica- Chalcedony and Jasper (variable) Agate: Bull's eye agate, Iris or fire agate, Onyx, Sardonyx. Bloodstone or heliotrope. Carnelian. Chrysoprase. Moss agate. Plasma. Prase. Sard. Jasper.
	Spinel (hardness: 8 Mohs) Magnesium aluminum oxide Specific gravity: 3.58-4.06 Balas ruby: Red Almandine spinel: Purple red Rubicelle: Orange Sapphire spinel and ghanospinel: Blue Chlorspinel: Green
Topaz.	Topaz (hardness: 8 Mohs) Aluminum silicate fluoride hydroxide Specific gravity: 3.5-3.6 Wine yellow, pale blue, green, violet, or red
Elbaite.	Tourmaline (hardness: 7-7.5 Mohs) Complex aluminum borosilicate (Elbaite, Dravite, Uvite) Specific gravity: 3.03-3.25 Achorite: Colorless Brazilian emerald: Green Dravite: Brown Indicolite: Dark blue Rubellite: Pink to red Siberite: Violet Verdilite: Green
Turquoise.	Turquoise (hardness: 5-6 Mohs) Hydrous copper aluminum phosphate Specific gravity: 2.6-2.8 Sky blue; greenish blue
Zircon.	Zircon (hardness: 7.5 Mohs) Zirconium silicate Specific gravity: 4.6-4.7 Jargon: Variable Matura diamond: Colorless Hyacinth: Yellow, orange, red, brown