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Name	Structure	Hardness	Specific Gravity	Refractive index	Doubly Refracting (bi-refraction)
Achroite ( Tourmaline )	Trigonal	7.5	3.06	1.62 - 1.64	0.018
Agate ( Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Albite	Triclinic	6	2.64	1.54 - 1.55	0.009
Almandine ( Garnet )	Cubic	7.5	4.00	1.76 - 1.83	None
Amber	Amorphous	2.5	1.08	1.54 - 1.55	Not Available
Amblygonite	Triclinic	6	3.02	1.57 - 1.60	0.026
Amethyst ( Quartz)	Trigonal	7	2.65	1.54 - 1.55	0.009
Andalusite	Orthorhombic	7.5	3.16	1.63 - 1.64	0.010
Andradite Garnet	Cubic	6.5	3.85	1.85 - 1.89	None
Anglesite	Orthorhombic	3	6.35	1.87 - 1.89	0.017
Apatite	Hexagonal	5	3.20	1.63- 1.64	0.003
Aquamerine ( Beryl )	Hexagonal	7.5	2.69	1.57 - 1.58	0.006
Aragonite	Orthorhombic	3.50	2.94	1.53 - 1.68	0.155
Aventurine ( Quartz )	Trigonal	7	2.65	1.54 - 1.55	0.009
Axinite	Triclinic	7	3.28	1.67 - 1.70	0.011
Azurite	Monoclinic	3.5	3.77	1.73 - 1.84	0.110
Barite	Orthorhombic	3	4.45	1.63 - 1.65	0.012
Benitoite	Hexagonal	6.5	3.67	1.76 - 1.80	0.047
Beryllonite	Monoclinic	5.5	2.83	1.55 - 1.56	0.009
Bloodstone ( Chalcedony )	Trigonal	7	2.61	1.53 - 1.54	0.004
Braziliznite	Monoclinic	5.5	2.99	1.60 - 1.62	0.021
Brown Quartz	Trigonal	7	2.65	1.54 - 1.55	0.009
Calcite	Trigonal	3	2.71	1.48 - 1.66	0.172
Carnelian ( Chalcedony )	Trigonal	7	2.61	1.53 - 1.54	0.004
Cassiterite	Tetragonal	6.5	6.95	2.00 - 2.10	0.100
Celestine	Orthorhombic	3.5	3.98	1.62 - 1.63	0.010
Cerussite	Orthorhombic	3.5	6.51	1.80 - 2.08	0.274
Chalcedony	Trigonal	7	2.61	1.53 - 1.54	0.004
Chatoyant Quartz	Trigonal	7	2.65	1.54 - 1.55	0.009
Chrysoberyl	Orthorhombic	8.5	3.71	1.74 - 1.75	0.009
Chrysocolla	Monoclinic	2	2.20	1.57 - 1.63	0.030
Chrysoprase (Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Citrine ( Quartz )	Trigonal	7	2.65	1.54 - 1.55	0.009
Coral	Trigonal	3	2.68	1.49 - 1.66	Not Available
Danburite	Orthorhombic	7	3.00	1.63 - 1.64	0.006
Datolite	Monoclinic	5	2.95	1.62 - 1.65	0.044
Diamond	Cubic	10	3.52	2.42	None
Diopside	Monoclinic	5.5	3.29	1.66 - 1.72	0.029
Dioptase	Trigonal	5	3.31	1.67 - 1.72	0.053
Dolomite	Trigonal	3.5	2.85	1.50 - 1.68	0.179
Dravite ( Tourmaline)	Trigonal	7.5	3.06	1.61 - 1.63	0.018
Dumortierite	Orthorhombic	7	3.28	1.69 - 1.72	0.037
Emerald ( Beryl )	Hexagonal	7.5	2.71	1.57 - 1.58	0.006
Enstatite	Orthorhombic	5.5	3.27	1.66 - 1.67	0.010
Epidote	Monoclinic	6.5	3.40	1.74 - 1.78	0.035
Euclase	Monoclinic	7.50	3.10	1.65 - 1.67	0.019
Fire Agate (Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Fluorite	Cubic	4	3.18	1.43	None
Gold	Cubic	2.5	19.30	None	None
Goshenite (Beryl)	Hexagonal	7.5	2.80	1.58 - 1.59	0.008
Grossular (Garnet)	Cubic	7	3.49	1.69 - 1.73	none
Gypsum	Monoclinic	2	2.32	1.52 - 1.53	0.010
Hambergite	Orthorhombic	7.5	2.35	1.55 - 1.63	0.072
Hauyne	Cubic	6	2.40	1.50	none
Heliodor ( Beryl )	Hexagonal	7.5	2.80	1.57 - 1.58	0.005
Hematite	Trigonal	6.5	5.20	2.94 - 3.22	0.280
Hessonite (grosular garnet)	Cubic	7.25	3.65	1.73 - 1.75	none
Howlite	Monoclinic	3.5	2.58	1.58 - 1.59	0.022
Hypersthene	Orthorhombic	5.5	3.35	1.65 - 1.67	0.010
Indicolite ( tourmaline)	Trigonal	7.5	3.06	1.62 - 1.64	0.018
Iolite	Orthorhombic	7	2.63	1.53 - 1.55	0.010
Ivory	Amorphous	2.5	1.90	1.53 - 1.54	not available
Jadeite	Monoclinic	7	3.33	1.66 - 1.68	0.012
Jasper (Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Jet	Amorphous	2.5	1.33	1.64 - 1.68	not availble
Kornerupine	Orthorhombic	6.5	3.32	1.66 - 1.68	0.013
Kyanite	Triclinic	5 or 7	3.68	1.71 - 1.73	0.017
Labradorite	Triclinic	6	2.70	1.56 - 1.57	0.010
Lapis Lazuli ( Lazurite)	various	5.5	2.80	1.5	none
Lazulite	Monoclinic	5.5	3.10	1.61 - 1.64	0.031
Malachite	Monoclinic	4	3.80	1.85	0.025
Meerschaum	Monoclinic	2.5	1.50	1.51 - 1.53	none
Microcline	Triclinic	6	2.56	1.52 - 1.53	0.008
Milky Quartz	Trigonal	7	2.65	1.54 - 1.55	0.009
Moonstone	Monoclinic	6	2.57	1.52 - 1.53	0.005
Morganite ( beryl)	Hexagonal	7.5	2.80	1.58 - 1.59	0.008
Nephrite ( jade)	Monoclinic	6.5	2.96	1.61 - 1.63	0.027
Obsidian	Amorphous	5	2.35	1.48 - 1.51	none
Oligoclase	Triclinic	6	2.64	1.54 - 1.55	0.007
Onyx	Trigonal	7	2.61	1.53 - 1.54	0.004
Opal	Amorphous	6	2.10	1.37 - 1.47	none
Orthoclase	Monoclinic	6	2.56	1.51 - 1.54	0.005
Padparasha ( Corundum)	Trigonal	9.00	4.00	1.76 - 1.77	0.008
Pearl	Orthorhombic	3	2.71	1.53 - 1.68	not availble
Peridot	Orthorhombic	6.50	3.34	1.64 - 1.69	0.036
Petalite	Monoclinic	6	2.42	1.50 - 1.51	0.014
Phenakite	Trigonal	7.5	2.96	1.65 - 1.67	0.015
Phoshophyllite	Monoclinic	3.50	3.10	1.59 - 1.62	0.021
Plasma ( Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Platinum	Cubic	4	21.40	none	none
Prase ( Chalcedony )	Trigonal	7	2.61	1.53 - 1.54	0.004
Prehnite	Orthorhombic	6	2.87	1.61 - 1.64	0.016
Pyrite	Cubic	6	4.90	none	none
Pyrope ( Garnet )	Cubic	7.25	3.80	1.72 - 1.76	none
Rhodochrosite	Trigonal	4	3.60	1.60 - 1.80	0.220
Rhodonite	Triclinic	6	3.60	1.71 - 1.73	0.014
Rock Crystal ( Quartz )	Trigonal	7	2.65	1.54 - 1.55	0.009
Rubellite ( Tourmaline)	Trigonal	7.5	3.06	1.62 - 1.64	0.018
Ruby ( Corundum)	Trigonal	9	4.00	1.76 - 1.77	0.008
Rutile	Tetragonal	6	4.25	2.62 - 2.90	0.287
Sapphire ( Corundum)	Trigonal	9	4.00	1.76 - 1.77	0.008
Sard	Trigonal	7	2.61	1.53 - 1.54	0.004
Sardonyx ( Chalcedony)	Trigonal	7	2.61	1.53 - 1.54	0.004
Scapolite	Tetragonal	6	2.70	1.54 - 1.58	0.020
Scheelite	Tetragonal	5	6.10	1.92 - 1.93	0.017
Schorl ( tourmaline)	Trigonal	7.5	3.06	1.62 - 1.67	0.018
Serpentine	Monoclinic	5	2.60	1.55 - 1.56	0.001
Shell	Various	2.5	1.30	1.53 - 1.59	not available
Sillimanite	Orthorhombic	7.5	3.25	1.66 - 1.68	0.019
Silver	Cubic	2.5	10.50	none	none
Sinhalite	Orthorhombic	6.5	3.48	1.67 - 1.71	0.038
Smithsonite	Triagonal	5	4.35	1.62 - 1.85	0.230
Sodalite	Cubic	5.5	2.27	1.48	none
Spessarite ( garnet)	Cubic	7	4.16	1.79 - 1.81	none
Sphalerite	Cubic	3.5	4.09	2.36 - 2.37	none
Spinel	cubic	8	3.60	1.71 - 1.73	none
Spodumene	Monoclinic	7	3.18	1.66 - 1.67	0.015
Staurolite	Orthorhombic	7	3.72	1.74 - 1.75	0.013
Taaefeite	hexagonal	8	3.61	1.72 - 1.77	0.004
Tektites	Amorphous	5	2.40	1.48 - 1.51	none
Titanite (sphene)	Monoclinic	5	3.53	1.84 - 2.03	0.120
Topaz	Orthorhombic	8	3.54	1.62 - 1.63	0.010
Tugtupite	Tetragonal	6	2.40	1.49 - 1.50	0.006
Turquise	Triclinic	6	2.80	1.61 - 1.65	0.040
Uvarite (Garnet)	Cubic	7.5	3.77	1.86 - 1.87	none
Vesuvianite ( Idocrase )	Tetragonal	6.50	3.40	1.70 - 1.75	0.005
Watermelon Tourmaline	Trigonal	7.5	3.06	1.62 - 1.64	0.018
Zircon	Tetragonal	7.5	4.69	1.93 - 1.98	0.059
Zoisite	Orthorhombic	6.5	3.35	1.69 - 1.70	0.010