ClassicGems.net

Hardness of Gems

Mineral hardness is a physical characteristic that can be tested, measured and compared to other minerals. One method is to test the hardness of one mineral against another. This is done through the ability of a harder material to scratch a softer one.

The Mohs' Hardness Scale rates the hardness of a mineral relative to others. It was created by German mineralogist Friedrich Mohs. The Mohs' Scale is one of several definitions of hardness in materials science. Mohs based his scale on ten readily available minerals. The minerals are registered on the scale by finding the hardest material they can scratch. The Mohs' scale is relative, not proportional.

The table below compares Mohs' hardness to Absolute hardness (as measured by a sclerometer). The Mohs' scale is relative, meaning it is a purely ordinal scale which lists the minerals in order of hardness but does not show differences of hardness between the minerals as each mineral is only one unit away from the next. This would indicate that Quartz is only 7 times harder than Talc and Diamond is only 10 times harder than Talc.

The Absolute hardness scale is proportional showing a quantitative difference between the minerals. This indicates that Quartz is actually 100 times harder than Talc and Diamond is actually 1500 times harder than Talc.

Mohs' Hardness

Mineral

Absolute Hardness

1

Talc

1

2

Gypsum

3

3

Calcite

9

4

Fluorite

21

5

Apatite

48

6

Orthoclase

72

7

Quartz

100

8

Topaz

200

9

Corundum

400

10

Diamond

1500

See table below for a more complete list of Moh's hardness.

Testing the Hardness of Minerals

The sclerometer is a mineralogist's instrument used to measure the hardness of minerals. The name sclerometer is from the Greek word skleros meaning hard.

The instrument is designed to determine the degree of hardness of a given mineral by applying pressure on a moving diamond point until a "scratch" has occurred.

Different Methods of Hardness Testing  -  There are four typical methods for testing the hardness of materials. These are the sclerometer method introduced by Turner in 1896; the scleroscope method recently invented by Shore; the indentation test adopted by Brinell about 1900; and the drill test introduced by Keep a few years earlier. Turner's Sclerometer is the method used to test the hardness of minerals. The other three methods are typically used to test metals only instead of minerals.

Turner's Sclerometer  - In this form of test a weighted diamond point is drawn, once forward and once backward, over the smooth surface of the material to be tested. The hardness number is the weight in grams required to produce a standard scratch. The scratch selected is one which is just visible to the naked eye as a dark line on a bright reflecting surface. It is also the scratch which can just be felt with the edge of a quill when the latter is drawn over the smooth surface at right angles to a series of such scratches produced by regularly increasing weights.

Moh's Hardness Table

Diamond
Moissanite
Corundum
Chrysoberyl
Cubic Zirconia
Rhodizite
YAG
Painite
Spinel
Taaffeite
Topaz
Beryl Family
Gahnite
Gahnospinel
Phenakite
Almandite Garnet
Euclase
Hambergite
Sapphirine
Zircon (high, med.)
Andalusite
Boracite
Iolite
Pyrope Garnet
Rhodolite Garnet
Spessartite Garnet
Simpsonite
Staurolite
Tourmaline
Chambersite
Danburite
Dumortierite
Grossular Garnet
Quartz
Euclase
Jeremejevite
Andradite Garnet
Axinite
Chalcedony
Diaspore
Jadeite
Peridot
Saussurite
Kornerupine
Nambulite
Pollucite
Scapolite
Zircon (low)
Cassiterite
Clinozoisite
Epidote
Idocrase
Sillimanite
Sinhalite
Spodumene Family
Tanzanite
Zoisite
Benitoite
Feldspar Family
Nephrite
Marcasite
Oligoclase
Orthoclase
Prehnite
Pyrite
Rutile
Sugilite
Amblygonite
Clinohumite
Labradorite
Petalite
Zektzerite
Bustamite
Diopside
Hematite
Manganotantalite
Opal
Rhodonite
Tektite
Anatase
Beryllonite
Hackmanite
Hauyne
Lazulite
Leucite
Milarite
Pyroxmangite
Actinolite
Brazilianite
Moldavite
Thomsonite
Willemite
Ekanite
Charoite
Chlorastrolite
Enstatite
Glass
Lazurite
Neptunite
Sodalite
Strontium Titanate
Turquoise
Datolite
Eudialyte
Herderite
Microlite
Monazite
Obsidian
Sellaite
Sphene
Apatite
Scheelite
Dioptase
Eosphorite
Apophyllite
Augelite
Legrandite
Synthetic Opal
Yugawaralite
Smithsonite
Zincite
Kyanite
Tugtupite
Friedelite
Triphylite
Variscite
Xenotime
Augelite
Creedite
Fluorite
Magnesite
Siderite
Aragonte
Azurite
Coral
Cuprite
Dolomite
Malachite
Powellite
Rhodochrosite
Sphalerite
Adamite
Thaumasite
Weloganite
Barite
Boleite
Celestite
Cerussite
Millerite
Witherite
Calcite
Verdite
Hemetite
Pearl
Jet
Crysocolla
Serpentine
Anglesite
Crocoite
Vanadinite
Wulfenite
Pyrargyrite
Amber
Proustite
Gypsum
Alabaster
Stichtite
Soapstone
Pyrophyllite

10
9.25
9
8.5
8.5
8.5
8.25
8
8
8
8
7.5 - 8
7.5 - 8
7.5 - 8
7.5 - 8
7.5
7.5
7.5
7.5
7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7 - 7.5
7
7
7
7
7
6.5 - 7.5
6.5 - 7.5
6.5 - 7
6.5 - 7
6.5 - 7
6.5 - 7
6.5 - 7
6.5 - 7
6.5 - 7
6.5
6.5
6.5
6.5
6.5
6 - 7
6 - 7
6 - 7
6 - 7
6 - 7
6 - 7
6 - 7
6 - 7
6 - 7
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6 - 6.5
6
6
6
6
6
5.5 - 6.5
5.5 - 6.5
5.5 - 6.5
5.5 - 6.5
5.5 - 6.5
5.5 - 6.5
5.5 - 6.5
5.5 - 6
5.5 - 6
5.5 - 6
5.5 - 6
5.5 - 6
5.5 - 6
5.5 - 6
5.5 - 6
5.5
5.5
5.5
5.5
5.5
5 - 6.5
5 - 6
5 - 6
5 - 6
5 - 6
5 - 6
5 - 6
5 - 6
5 - 6
5 - 6
5 - 5.5
5 - 5.5
5 - 5.5
5 - 5.5
5 - 5.5
5 - 5.5
5 - 5.5
5 - 5.5
5
5
5
5
4.5 - 5
4.5 - 5
4.5
4.5
4.5
4 - 4.5
4 - 4.5
4 - 7
4 - 6.5
4 - 5
4 - 5
4 - 5
4 - 5
4
4
4
3.5 - 4.5
3.5 - 4.5
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5 - 4
3.5
3.5
3.5
3 - 3.5
3 - 3.5
3 - 3.5
3 - 3.5
3 - 3.5
3 - 3.5
3
3
2.5 - 6
2.5 - 4.5
2.5 - 4
2 - 4
2 - 4
2.5 - 3
2.5 - 3
2.5 - 3
2.5 - 3
2.5
2 - 2.5
2 - 2.5
2
2
1.5 - 2
1 - 2.5
1 - 2