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

 

Emerald

7½-8

Pyrite

6-6½

Almandite

6½-7½

Enstatite

Pyrolusite

6-6

Amazonite

6-6½

Eosphorite

5

Pyrope

6½-7½

Amber

2-2½

Epidote

6-7

Quartz

7

Amblygonite

6

Euclase

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

Glass

5

Sanidine

6

Andesine

6-6½

Gold

2½-3

Sapphire

9

Andradite

6½-7½

Grossularite

6½-7½

Scapolite

5½-6

Anhydrite

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

Barite

3-3½

Hypersthene

5-6

Smithsonite

5

Benitoite

6-6½

Idocrase

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

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

Moldavite

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

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

Pearl

2½-4½

Willemite

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 schiller 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.

 

 

 

 

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