Physical And Optical Properties Of Minerals And Gemstones

Physical & Optical Properties of Minerals & Gemstones

Hardness

Hardness: The resistance to abrading or scratching; measured from 1 to 10 on the Mohs Scale.

Mohs Hardness Scale

1.	Can be scratched easily with a fingernail.	Talc: 1 Sulfur: 1 ½-2
2.	Can be scratched with a fingernail.	Gypsum: 2 Mica: 2 - 2 ½
3.	Can be scratched with a coin.	Calcite: 3 Pearl: 3-4
4.	Can be scratched easily with a knife; cannot scratch glass.	Rhodochrosite: 4 Fluorite: 4
5.	Can be scratched with a knife; can just scratch glass.	Lapis Lazuli: 5-6 Apatite: 5 Turquoise: 5-6 Opal: 5 ½-6 ½
6.	Can be scratched with a steel file; easily scratches window/bottle glass.	Feldspar: 6-6 ½ Pyrite: 6 ½ Tanzanite: 6 ½-7 Zircon: 6 ½-7 ½ Peridot: 6 ½-7 Moonstone: 6-6 ½
7.	Easily scratches metal, glass, and softer stones.	Quartzes: 7 Tourmaline: 7-7 ½ Garnet: 7-7 ½ Beryls: 7 ½-8
8.	Scratches Quartz and softer stones.	Topaz: 8 Chrysoberyl: 8 ½
9.	Scratches Topaz and softer stones.	Ruby: 9 Sapphire: 9
10.	Scratches Ruby and Sapphire.	Diamond: 10

The Hardness Values of Various Minerals & Gemstones

Mineral	Mohs	Mineral	Mohs	Mineral	Mohs

Actinolite	5½-6	Dolomite	3½-4	Proustite	2-2½
Agate	6½-7	Dumortierite	7½-8½	Purpurite	4-4½
Alexandrite	8½	Emerald	7½-8	Pyrite	6-6½
Almandite	6½-7½	Enstatite	5½	Pyrolusite	6-6
Amazonite	6-6½	Eosphorite	5	Pyrope	6½-7½
Amber	2-2½	Epidote	6-7	Quartz	7
Amblygonite	6	Euclase	7½	Rhodochrosite	4
Amethyst	7	Fluorite	4	Rhodonite	5½-6½
Ammonite	4	Garnet	6½-7½	Rose Quartz	7
Analcite	5-5½	Gaspeite	4½-5	Ruby	9
Anatase	5½-6	Gaylussite	2½-3	Rutile	6-6½
Andalusite	7½	Glass	5	Sanidine	6
Andesine	6-6½	Gold	2½-3	Sapphire	9
Andradite	6½-7½	Grossularite	6½-7½	Scapolite	5½-6
Anhydrite	3½	Gypsum	2	Scheelite	4½-5
Apatite	5	Hauynite	5½-6	Selenite	2
Apophyllite	4½-5	Heliodor	7½-8	Serpentine	2½-5½
Aquamarine	7½-8	Hematite	5½-6½	Siderite	3½-4½
Aragonite	3½-4	Hemimorphite	5	Silver	2½-3
Aventurine	7	Hessonite	6½-7½	Simpsonite	7-7½
Axinite	6½-7	Hiddenite	6½-7	Sinhalite	6½-7
Azurite	3½-4	Howlite	3-3½	Smaragdite	5½
Barite	3-3½	Hypersthene	5-6	Smithsonite	5
Benitoite	6-6½	Idocrase	6½	Smoky Quartz	7
Beryl	7½-8	Iolite	7-7½	Sodalite	5½-6
Beryllonite	5½-6	Jadeite	6½-7	Spessartite	6½-7½
Bixbite	7½-8	Jasper	6½-7	Sphalerite	3½-4
Boracite	7-7½	Kornerupine	6½-7	Sphene	5-5½
Brazilianite	5½	Kunzite	6½-7	Spinel	8
Calcite	3	Kyanite	4-7*	Stichtite	1½-2½
Cancrinite	5-6	Labradorite	6-6½	Sugilite	6-6½
Cassiterite	6-7	Lapis Lazuli	5-6	Sulfur	1½-2½
Celestite	3-3½	Lazulite	5-6	Taaffeite	8
Cerussite	3-3½	Leucite	5½-6	Talc	1
Chalcedony	6½-7	Magnesite	3½-4½	Tantalite	6-6½
Chalcopyrite	3½-4	Magnetite	5½-6½	Tanzanite	6½-7
Charoite	5-6	Malachite	3½-4	Tiger's Eye	6½-7
Chrysoberyl	8½	Moldavite	5½	Topaz	8
Chrysocolla	2-4	Moonstone	6-6½	Tourmaline	7-7½
Chrysoprase	6½-7	Morganite	7½-8	Tremolite	5-6
Cinnabar	2-2½	Natrolite	5-5½	Tugtupite	5½-6
Citrine	7	Nephrite	6-6½	Turquoise	5-6
Colemanite	4½	Obsidian	5-5½	Ulexite	2-2½
Copper	2½-3	Onyx	7	Uvarovite	6½-7½
Coral	3-4	Opal	5½-6½	Variscite	4-5
Crocoite	2½-3	Orthoclase	6-6½	Vivianite	1½ -2
Cubic Zirconia	8½	Pearl	2½-4½	Willemite	5½
Cuprite	3½-4	Periclase	5½-6	Witherite	3-3½
Danburite	7-7½	Peridot	6½-7	Wolframite	5-5½
Datolite	5-5½	Petalite	6-6½	Wulfenite	3
Demantoid	6½-7½	Phenakite	7½-8	Zincite	4-5
Diamond	10	Phosgenite	2-3	Zircon	6½-7½
Diaspore	6½-7	Pollucite	6½-7	Zoisite	6-6½
Diopside	5-6	Prasiolite	7
Dioptase	5	Prehnite	6- 6½

**Please note that some minerals, such as Kyanite, have different hardness values on different crystals faces and in different directions. This cutting resistance is of utmost importance to gem cutters.

Density ~ Specific Gravity

Specific Gravity: This is the weight ratio of a mineral due to the density of the atomical arrangement and the heaviness of the elements it contains. There are specialized instruments able to measure these values.

The Specific Gravity Values of Various Minerals & Gemstones

Mineral	SG	Mineral	SG

Actinolite	3.30-3.07	Kyanite	3.53-3.70
Aegirine	3.40-3.55	Labradorite	2.65-2.75
Agate	2.60-2.64	Lapis Lazuli	2.50-3.00
Almandite	3.93-4.30	Lazulite	3.04-3.14
Amazonite	2.56-2.58	Leucite	2.45-2.50
Amber	1.05-1.09	Magnetite	5.17
Amblygonite	3.01-3.11	Malachite	3.25-4.10
Amethyst	2.65	Moldavite	2.32-2.38
Ammonite	2.75-2.80	Moonstone	2.56-2.59
Analcite	2.22-2.29	Muscovite	2.78-2.88
Andalusite	3.05-3.20	Natrolite	2.20-2.26
Andesine	2.65-2.69	Nephrite	2.90-3.03
Andradite	3.7-4.1	Obsidian	2.35-2.60
Anhydrite	2.90-2.98	Opal	1.98-2.50
Apatite	3.16-3.23	Orthoclase	2.55-2.63
Apophyllite	2.30-2.50	Pearl	2.60-2.85
Aquamarine	2.68-2.74	Periclase	3.7-3.9
Aragonite	2.94	Peridot	3.28-3.48
Aventurine	2.64-2.69	Petalite	2.40
Axinite	3.26-3.36	Phenakite	2.95-2.97
Azurite	3.7-3.9	Phosgenite	6.13
Barite	4.43-4.46	Pollucite	2.85-2.94
Benitoite	3.64-3.68	Prasiolite	2.65
Beryl	2.66-2.87	Prehnite	2.82-2.94
Beryllonite	2.80-2.87	Proustite	5.51-5.64
Brazilianite	2.98-2.99	Purpurite	3.2-3.4
Calcite	2.69-2.71	Pyrite	5.00-5.20
Cancrinite	2.42-2.51	Pyrolusite	4.5-5.0
Cassiterite	6.7-7.1	Pyrope	3.62-3.87
Celestite	3.97-4.00	Quartz	2.65
Cerussite	6.46-6.57	Rhodochrosite	3.45-3.70
Chalcedony	2.58-2.64	Rhodonite	3.40-3.74
Chalcopyrite	4.10-4.30	Rose Quartz	2.65
Charoite	2.54-2.78	Ruby	3.97-4.05
Chrysoberyl	3.70-3.78	Rutile	4.20-4.30
Chrysocolla	2.00-2.40	Sanidine	2.56-2.62
Chrysoprase	2.58-2.64	Sapphire	3.95-4.03
Cinnabar	8.0-8.2	Scapolite	2.57-2.74
Citrine	2.65	Scheelite	5.9-6.3
Colemanite	2.40-2.42	Selenite ~ Gypsum	2.31-2.32
Copper	8.94-8.95	Serpentine	2.44-2.62
Coral	2.60-2.70	Siderite	3.83-3.96
Crocoite	5.9-6.1	Silver	9.6-12.0
Cubic Zirconia	5.5-5.9	Simpsonite	5.92-6.84
Cuprite	5.85-6.15	Sinhalite	3.46-3.50
Danburite	2.97-3.03	Smaragdite	3.24-3.50
Datolite	2.90-3.00	Smithsonite	4.00-4.65
Diamond	3.50-3.53	Smoky Quartz	2.65
Diaspore	3.30-3.39	Sodalite	2.14-2.40
Diopside	3.22-3.38	Spessartite	4.12-4.18
Dioptase	3.28-3.35	Sphalerite	3.90-4.10
Dolomite	2.80-2.95	Sphene	3.52-3.54
Dumortierite	3.26-3.41	Spinel	3.54-3.63
Emerald	2.67-2.78	Staurolite	3.65-3.77
Enstatite	3.20-3.30	Stichtite	2.16-2.18
Epidote	3.3-3.5	Sugilite	2.76-2.80
Euclase	3.10	Sulfur	2.05-2.08
Fluorite	3.00-3.25	Taaffeite	3.60-3.62
Gaylussite	1.99	Talc	2.55-2.80
Gold	15.5-19.3	Tantalite	5.18-8.20
Grossularite	3.57-3.73	Tanzanite	3.35
Hauynite	2.4-2.5	Tiger's Eye	2.58-2.64
Hematite	5.12-5.28	Topaz	3.49-3.57
Hemimorphite	3.30-3.50	Tourmaline	2.82-3.32
Hiddenite	3.15-3.21	Tremolite	2.95-3.07
Hornblende	2.9-3.4	Tugtupite	2.36-2.57
Howlite	2.45-2.58	Turquoise	2.31-2.84
Hypersthene	3.4-3.5	Ulexite	1.65-1.95
Idocrase	3.32-3.47	Uvarovite	3.77
Iolite	2.58-2.66	Variscite	2.42-2.58
Ivory	1.7-2.0	Willemite	3.89-4.18
Jadeite	3.30-3.38	Witherite	4.27-4.35
Jasper	2.58-2.91	Wolframite	7.1-7.6
Jet	1.19-1.35	Wulfenite	6.50-7.00
Kornerupine	3.27-3.45	Zincite	5.66
Kunzite	3.15-3.21	Zircon	3.93-4.73

Cleavage and Fracture

Cleavage: The tendency of a mineral to break along a plane due to a direction of weakness in the crystal.

Fracture: A break with an uneven or irregular surface crack.

Minerals and gemstones can be split along certain flat planes which are called cleavage. Cleavage is related to the lattice (the cohesive property of the atoms) of the crystal. The ease with which a crystal can be cleaved is referred to as being either: perfect, good, or imperfect. Some may not be cleaved at all and are referred to as not having cleavage.

A crystal or gemstone can be broken with a blow which produces irregular surfaces called fractures. Fractures are referred to as being either: conchoidal (shell-like), uneven, smooth, fibrous, splintery, or grainy. Both the type of cleavage and type of fracture a mineral has is important when trying to identify a mineral. Knowing these values is also extremely helpful to lapidaries and stone setters.

Tenacity

Tenacity: The strength of a mineral. It is also its resistance to breaking, crushing, bending, crumbling, tearing, or changing shape. There are several different terms used to denote a mineral’s tenacity. They are listed below.

Elastic: It can be bent and will resume its previous shape when let go.

Ductile: It can be pulled and made into very thin threads.

Flexible: It can easily be bent without breaking and can be shaped.

Fragile: It will easily break into pieces.

Friable: It crumbles easily.

Malleable: It can be flattened out into thin sheets without breaking.

Sectile: It can be cut into shavings with a blade.

Optical Properties ~ Streak

Streak: A mineral's powder color. It is most easily observed by rubbing the mineral on a piece of white unglazed porcelain, which is known as a streak plate.

The Streak Colors of Various Minerals

White, Colorless, Light Gray

Actinolite, Agate, Alabaster, Alexandrite, Almandite, Amazonite, Amber, Amblygonite, Amethyst, Anatase, Andalusite, Andradite, Anhydrite, Apatite, Apophyllite, Aquamarine, Aragonite, Augelite, Aventurine, Axinite, Barite, Barytocalcite, Benitoite, Beryllonite, Brazilianite, Calcite, Cancrinite, Carnelian, Cassiterite, Cerussite, Chalcedony, Charoite, Chrysoberyl, Chrysoprase, Citrine, Celestite, Colemanite, Coral, Cubic Zirconia, Danburite, Datolite, Demantoid, Diamond, Diopside, Dolomite, Dumorteirite, Emerald, Enstatite, Epidote, Euclase, Fluorite, Gahnite, Gaylussite, Glass, Grossularite, Hambergite, Hauynite, Hemimorphite, Hessonite, Hiddenite, Howlite, Hypersthene, Idocrase, Iolite, Ivory, Jadeite, Jasper, Kornerupine, Kunzite, Kurnakovite, Kyanite, Labradorite, Lazulite, Leucite, Linobate, Magnesite, Meerschaum, Milarite, Mimetite, Moldavite, Monazite, Moonstone, Montebrasite, Moss Agate, Natrolite, Nephrite, Obsidian, Opal, Orthoclase, Parisite, Periclase, Peridot, Peristerite, Pearl, Petalite, Phenakite, Phosgenite, Prasiolite, Precious Beryl, Prehnite, Pyrope, Quartz, Rhodochrosite, Rhodonite, Rose Quartz, Ruby, Sanidine, Sapphire, Scapolite, Scheelite, Serpentine, Siderite, Silver, Sinhalite, Smithsonite, Smoky Quartz, Sodalite, Spessartite, Sphene, Spinel, Spodumene, Staurolite, Tanzanite, Topaz, Tourmaline, Tremolite, Turquoise, Tugtupite, Ulexite, Uvarovite, Variscite, Willemite, Witherite, Wulfenite, Zircon, and Zoisite

Red, Pink, Orange

Cinnabar, Crocoite, Cuprite, Friedelite, Greenockite, Hematite, Manganotantalite, Piemontite, Proustite, Purpurite, Pyargyrite, Pyroxmangite, and Realgar

Yellow, Orange, Brown

Chromite, Descloizite, Durangite, Fergusonite, Gold, Hubnerite, Jet, Neptunite, Rutile, Sulfur, Sphalerite, Stibiotantalite, Thorianite, Tiger’s Eye, Vanadinite, Wurtzite, and Zincite

Green, Yellow-Green, Blue-Green

Bayldonite, Chrysocolla, Dioptase, Gadolinite, Gaspeite, Hornblende, Malachite, and Marcasite

Blue, Blue-Green, Blue-Red

Azurite, Boleite, Ceruleite, Euxenite, Lapis Lazuli, Linarite, Shattuckite, and Vivianite

Black, Gray

Anthophyllite, Aschynite, Bixbyite, Chalcopyrite, Davidite, Ilmenite, Ilvaite, Magnetite, Melonite, Pyrite, Pyrolusite, Tantalite, and Wolframite

Optical Properties ~ Refraction

Refraction: The bending of light (or any wave phenomenon) when it moves between media with different conductive velocities.

Refractive Index: A mathematical constant equal to the ratio of the velocity of light in a vacuum to that in the substance; it determines the angle at which light bends when it enters a substance obliquely. There are methods of measuring these values also.

Double Refraction: A phenomenon which occurs when the ray of light entering a crystal is refracted and divided into two rays instead of one. This is most commonly seen in Calcite and Zircon.

The Refractive Indices of Various Gemstones

Mineral	RI	Mineral	RI

Actinolite	1.614-1.653	Jet	1.640-1.680
Adamite	1.708-1.760	Kornerupine	1.660-1.699
Aegirine	1.700-1.800	Kunzite	1.660-1.681
Agate	1.530-1.540	Kyanite	1.710-1.734
Almandite	1.770-1.820	Labradorite	1.559-1.570
Amazonite	1.522-1.530	Lapis Lazuli	1.50
Amber	1.539-1.545	Lazulite	1.612-1.646
Amblygonite	1.578-1.646	Legrandite	1.675-1.740
Amethyst	1.544-1.553	Leucite	1.504-1.509
Ammonite	1.52-1.68	Magnesite	1.509-1.717
Analcite	1.479-1.489	Malachite	1.655-1.909
Anatase	2.488-2.564	Mimetite	2.120-2.135
Andalusite	1.627-1.649	Moldavite	1.49-1.51
Andesine	1.543-1.551	Montebrasite	1.594-1.633
Andradite	1.88-1.94	Moonstone	1.518-1.526
Anglesite	1.878-1.895	Natrolite	1.480-1.493
Anhydrite	1.570-1.614	Nepheline	1.526-1.546
Apatite	1.628-1.649	Nephrite	1.600-1.627
Apophyllite	1.535-1.537	Neptunite	1.690-1.736
Aquamarine	1.564-1.596	Obsidian	1.45-1.55
Aragonite	1.530-1.685	Oligoclase	1.542-1.549
Aventurine	1.544-1.553	Opal	1.37-1.52
Axinite	1.656-1.704	Painite	1.787-1.816
Azurite	1.720-1.848	Parisite	1.671-1.772
Barite	1.636-1.648	Pearl	1.53-1.69
Benitoite	1.757-1.804	Pectolite	1.595-1.645
Beryl	1.562-1.602	Periclase	1.74
Beryllonite	1.552-1.561	Peridot	1.650-1.703
Boracite	1.658-1.673	Petalite	1.502-1.519
Brazilianite	1.602-1.623	Phenakite	1.650-1.670
Brookite	2.583-2.700	Phosgenite	2.114-2.145
Bustamite	1.662-1.707	Pollucite	1.517-1.525
Calcite	1.486-1.658	Prasiolite	1.544-1.553
Cancrinite	1.495-1.528	Prehnite	1.611-1.669
Cassiterite	1.997-2.098	Proustite	2.881-3.084
Celestite	1.619-1.635	Purpurite	1.85-1.92
Cerussite	1.804-2.079	Pyrargyrite	2.88-3.08
Chalcedony	1.530-1.540	Pyrope	1.720-1.756
Charoite	1.550-1.561	Quartz	1.544-1.553
Chrysoberyl	1.746-1.763	Rhodizite	1.690
Chrysocolla	1.460-1.570	Rhodochrosite	1.600-1.820
Chrysoprase	1.530-1.540	Rhodonite	1.716-1.752
Cinnabar	2.905-3.256	Rose Quartz	1.544-1.553
Citrine	1.544-1.553	Ruby	1.762-1.778
Clinohumite	1.629-1.674	Rutile	2.616-2.903
Clinozoisite	1.670-1.734	Sanidine	1.518-1.530
Colemanite	1.586-1.615	Sapphire	1.762-1.778
Coral	1.486-1.658	Scapolite	1.540-1.579
Creedite	1.461-1.485	Scheelite	1.918-1.937
Crocoite	2.29-2.66	Scolecite	1.509-1.525
Cubic Zirconia	2.088-2.176	Serpentine	1.560-1.571
Cuprite	2.849	Shattuckite	1.752-1.815
Danburite	1.630-1.636	Siderite	1.633-1.875
Datolite	1.621-1.675	Simpsonite	1.976-2.034
Diamond	2.417-2.419	Sinhalite	1.665-1.712
Diaspore	1.702-1.750	Smithsonite	1.621-1.849
Diopside	1.664-1.730	Smoky Quartz	1.544-1.553
Dioptase	1.644-1.709	Sodalite	1.48
Dolomite	1.502-1.698	Spessartite	1.790-1.820
Dumortierite	1.678-1.689	Sphalerite	2.368-2.371
Emerald	1.565-1.602	Sphene	1.843-2.110
Enstatite	1.650-1.680	Spinel	1.712-1.762
Eosphorite	1.638-1.671	Spurrite	1.637-1.681
Epidote	1.729-1.768	Staurolite	1.736-1.762
Euclase	1.650-1.677	Stichtite	1.516-1.544
Eudialyte	1.591-1.633	Strontianite	1.52-1.67
Fluorite	1.434	Sugilite	1.607-1.611
Gahnite	1.791-1.818	Sulfur	1.958-2.245
Gaylussite	1.443-1.523	Taaffeite	1.719-1.730
Glass	1.44-1.90	Talc	1.54-1.59
Grossularite	1.734-1.759	Tantalite	2.26-2.43
Gypsum	1.520-1.529	Tanzanite	1.691-1.700
Hambergite	1.553-1.628	Thomsonite	1.515-1.542
Hauynite	1.496-1.510	Tiger's Eye	1.534-1.540
Hematite	2.940-3.220	Topaz	1.609-1.643
Hemimorphite	1.614-1.636	Tourmaline	1.614-1.666
Herderite	1.587-1.627	Tremolite	1.560-1.643
Hessonite	1.730-1.757	Tugtupite	1.496-1.502
Hiddenite	1.660-1.681	Turquoise	1.610-1.650
Hodgkinsonite	1.719-1.748	Ulexite	1.491-1.520
Howlite	1.586-1.605	Uvarovite	1.87
Hypersthene	1.673-1.731	Variscite	1.563-1.594
Idocrase	1.700-1.723	Vivianite	1.560-1.640
Iolite	1.542-1.578	Willemite	1.690-1.723
Ivory	1.535-1.570	Witherite	1.529-1.677
Jadeite	1.652-1.688	Wulfenite	2.280-2.400
Jasper	1.54	Zincite	2.013-2.029
Jeremejevite	1.637-1.653	Zircon	1.810-2.024

Optical Properties ~ Dispersion

Dispersion: This is the splitting of light as it enters a gemstone. Colors separate during refraction of white light, which leads to seeing “fire” in a gem.

Dispersion Values of Various Gemstones

Gemstone	Dispersion	Gemstone	Dispersion

Almandite	0.027	Hemimorphite	0.020
Amblygonite	0.014-0.015	Herderite	0.017
Amethyst	0.013	Hessonite	0.027
Ametrine	0.013	Hiddenite	0.017
Anatase	0.213-0.259	Idocrase	0.019-0.025
Andalusite	0.016	Iolite	0.017
Andradite	0.057	Kornerupine	0.018
Anglesite	0.044	Kunzite	0.017
Apatite	0.013	Kyanite	0.020
Aquamarine	0.014	Labradorite	0.019
Aventurine	0.013	Leucite	0.010
Axinite	0.018-0.020	Peridot	0.020
Barite	0.016	Phenakite	0.015
Benitoite	0.046	Pollucite	0.012
Beryl	0.014	Prasiolite	0.013
Beryllonite	0.010	Pyrope	0.022
Boracite	0.024	Quartz	0.013
Brazilianite	0.014	Rhodochrosite	0.015
Calcite	0.008-0.017	Rose Quartz	0.013
Cancrinite	0.010	Ruby	0.018
Cassiterite	0.071	Sapphire	0.018
Cerussite	0.055	Scapolite	0.017
Chrysoberyl	0.015	Scheelite	0.038
Citrine	0.013	Sillimanite	0.015
Clinozoisite	0.019	Sinhalite	0.018
Cubic Zirconia	0.065	Smithsonite	0.014-0.031
Danburite	0.017	Smoky Quartz	0.013
Datolite	0.016	Sodalite	0.018
Demantoid	0.057	Spessartite	0.027
Diamond	0.044	Sphalerite	0.156
Diopside	0.017-0.020	Sphene	0.051
Dioptase	0.036	Spinel	0.020
Ekanite	0.018	Staurolite	0.023
Emerald	0.014	Strontianite	0.008-0.028
Epidote	0.030	Tanzanite	0.030
Euclase	0.016	Topaz	0.014
Feldspar	0.012	Tourmaline	0.017
Fluorite	0.007	Whewellite	0.034
Grossularite	0.020	Willemite	0.027
Gypsum	0.033	Wulfenite	0.203
Hambergite	0.015	Zircon	0.039

Luster

Luster: The manner in which a mineral reflects light from its surface; it is affected by the surface’s smoothness and reflectivity. There are several different terms used to denote a mineral’s luster, which are described below.

Dull: Earthy and dull looking, as seen mainly in porous minerals.

Waxy: Looks like the surface of a candle, as seen in chalcedony.

Greasy: It almost appears to be wet and oily.

Pearly: Looks like the surface of a pearl and may have a play of colors.

Silky: A shiny surface like a piece of silk, as seen with some fibrous minerals.

Glassy ~ Vitreous: It looks like glass, as is seen in obsidian varieties.

Resinous: It looks like fresh shellac or resin.

Adamantine: A high brilliant diamond-like luster.

Sub-metallic: A silvery or metallic luster yet still transparent.

Translucent: Light can pass through it, but it is not transparent.

Transparent: Light can pass through it clearly.

Opaque: Light cannot pass through it at all.

Metallic: Very shiny and highly reflective, as seen in metals.

Why Are All of These Properties Important?

It is important for the collector of minerals and gemstones to know the different values and measurements of minerals and gemstones. These values are extremely important to geologists, mineralogists, gemologists, gem cutters, gem setters, and jewelers. Without knowing these values, it would be extremely difficult for anyone to be able to identify one mineral or gemstone from another. There are many different instruments and methods used to identify minerals. There are also several other important properties which are also very helpful in identifying minerals and gemstones. These additional properties include color, color changes, cleavage, absorption spectra, transparency, luster, pleochroism, luminescence, fluorescence, and other optical phenomena. Some of these additional phenomena are adularescence, asterism, aventurescence, chatoyancy, iridescence, labradorescence, opalescence, play-of-color, and various inclusions. Please refer to my "Geological and Mineralogical Glossary" page for the definitions of these terms. You may also refer to my "Fluorescent Minerals" and "Pleochroic, Color Change, Color Shift, & Multicolored Gems & Minerals" pages for additional information on these subjects.

How Do Minerals, Crystals, & Gems Get Their Colors?

Color results from a mineral’s chemical composition, impurities that may be present, and flaws or damage in the internal structure. Most minerals are usually white or colorless in a pure state. Many impurities can color these minerals and make their color variable. Some crystals get their color from growth imperfections. Growth imperfections interfere with light passing through the crystal making it appear darker or nearly black.

Idiochromatic minerals are "self colored" due to their composition. The color is a constant and predictable component of the mineral.

Allochromatic minerals are "other colored" due to trace impurities in their composition or defects in their structure. In this case, the color is a variable and unpredictable property of the mineral.

Pseudochromatic minerals are "false colored" due to tricks in light diffraction. The color is variable but a unique property of the mineral, such as the colors produced in precious opal and the shiller reflections in Sunstone and Labradorite.

**The most common trace elements/coloring elements in minerals are: Beryllium, Chromium, Cobalt, Copper, Iron, Lithium, Manganese, Nickel, Sulfur, Titanium, Uranium, and Vanadium.

Why Do Gemstones Have Different Colors?

Color is the most important characteristic of gemstones, though in the case of most Diamonds it is the absence of color which is most important. What is responsible for the variations in color?

Color is produced by the way a gemstone absorbs light. Light is an electromagnetic vibration at certain wavelengths, but the human eye can only perceive certain wavelengths. The field of the visible color spectrum includes red, orange, yellow, green, blue, and violet.

There are several different reasons why the various gemstone varieties absorb light differently. Some gemstones are said to be idiochromatic or self-colored. They absorb certain wavelengths of light due to characteristics of their chemical structure. Most gemstones are allochromatic. They are colored by impurities or trace elements in their crystal structure.

If all the different wavelengths of light pass through a gemstone, it will appear colorless. On the other hand, if the gem material absorbs all the light, it will be appear black. If a stone absorbs all wavelengths except those in the red part of the spectrum, the gem will appear red.

The relationship between a chemical impurity and a gemstone color is not a simple one. Sometimes a similar color can result from different trace elements. Also, a single trace element can produce different colors in different gem varieties. This is because there is a complex relationship between the gem's crystal structure and the trace elements.

Another way in which gemstones acquire color is through human intervention in the form of gem treatments. Heat treatment is often used to change the chemical state of an impurity to deepen or lighten color, reduce a certain hue, or improve clarity. Gemstones are also dyed, treated with chemicals, coated with chemicals or metals, irradiated, and artificially colored in many other ways to alter their appearance. All gemstone treatments must be disclosed by the vendor prior to the sale of the gemstone.

**To learn more about gemstone treatments, please refer to my "Gemstone Treatments, Enhancements, & Care" page.

Can The Color Of My Minerals Or Gemstones Fade?

The colors of some minerals and gemstones can be altered by time or exposure to sunlight or bright display lights. Some may fade, while others may oxidize. Some porous gems, such as Agate, Lapis Lazuli, Pearls, and Turquoise may be treated to stabilize their color. Gemstones that have had their color altered through the various treatments may also fade, change color, or become spotty over time.

Minerals & Gemstones Sensitive To Light

Upon exposure to different kinds of light many minerals and gemstones can undergo changes in color or transparency. Some may fade, while others can darken. Temporary color changes may also occur. Not all of a given gemstone or mineral will be sensitive to light. Sometimes a certain location/source will be the deciding factor. Also, certain color varieties or individual colors of a mineral or gem will be light sensitive. Other times all of a certain mineral or gem will be light sensitive. If in doubt, be aware that it can occur and take preventative measures to protect the mineral specimen or gemstone from prolonged light exposure. Even if a particular mineral that you have is not listed below, please keep an eye on it if it will be undergoing prolonged light exposure. Some minerals and gems, such as Hiddenite/Green Spodumene and Yellow Phenakite can fade within only one hour of exposure to bright light or sunlight!

These minerals, some of their family members, or some of their color varieties have been reported to show some type of sensitivity to light: Agate, Amazonite, Amethyst, Apatite, Aquamarine, Aragonite, Argentite, Barite, Bermanite, Beryl, Bromargyrite, Bustamite, Calcite, Celestite, Chalcopyrite, Chlorargyrite, Chrysoprase, Cinnibar, Citrine, Corderoite, Corundum/Sapphire, Crocoite, Creedite, Cuprite, Diamond, Fluorapatite, Fluorite, Hackmanite, Halite, Hiddenite/Green Spodumene, Inesite, Kunzite/Pink Spodumene, Lapis Lazuli, Marcasite, Microcline, Morganite, Morion Quartz, Opal, Orpiment, Pararealgar, Pearls, Phenakite, Prasiolite/Green Quartz, Proustite, Pyrargyrite, Pyrite, Realgar, Rose Quartz, Scapolite, Silver (Native), Smoky Quartz, Sodalite, Spinel, Stephanite, Terlinguacreekite, Tetrahedrite, Topaz, Tourmaline, Tugtupite, Turquoise, Vanadinite, Vivianite, Wulfenite, and Zircon.

**If the images and/or text on any of the web pages do not appear evenly spaced and centered on your screen, which commonly occurs with AOL pages, maximize the individual page's window. That should resolve the problem.