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Mohs Scale

Mohs Scale

The Mohs scale is not a scale that weighs gemstones. It is a scale that compares the hardness of gemstones. The hardness of gemstones is one of the most important properties of gemstones.

It is of inestimable value to the gemstone cutter, the gemstone setter, the wearer of jewelry, and is very important when you are investing in expensive antique gemstone engagement rings and antique gemstone jewelry that you would like to pass down in the family.

Discover the Meaning of Gemstones! Click Here!

Finds out the Diamond Facts! Click Here!

Mohs Scale of Hardness Test

Vienese mineralogist, Frederick Mohs (1773-1839) developed the comparison chart in the early 1800s that compares the hardness of ten easily accessible minerals. He introduced the term scratch hardness and set up a comparison scale using ten minerals of different degrees of hardness (Mohs' hardness scale) which is still widely used.

The hardness of a material measures how tightly the atoms are held together within it. This test is done either by scratching one substance with another and using the Moh's Scale. On the Moh's Scale, diamond is ranked 10 and graphite is ranked between 1 and 2. This suggests that diamond is about 40 times harder than graphite. All gemstones known to us today are allocated to Mohs hardness scale. The comparison chart begins with talc, it's 1 on the Mohs Scale and is the softest of the 10 gemstones.

The Mohs' hardness scale works up to diamond which is ranked the highest at 10 on the hardness scale. A girl's best friend, is also the traditional wedding anniversary gift for couples celebrating their 10th wedding anniversary.

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The 10 gemstones are ranked in order of their hardness. The minerals of higher numbers will scratch the minerals with lower numbers, makes sense- right?

For instance, a diamond at 10 on the Mohs scale will scratch a sapphire which is 9 on the hardness scale. Rubies and Sapphires are members of the corundum family in the list of gemstones.

Just because diamonds and sapphires are close on the hardness scale, this does not mean however they are close in hardness.

The Mohs' hardness scale is a relative hardness scale. It only shows which gemstone is harder than another one. Although a diamond at 10, will scratch a ruby or a sapphire at 9, diamonds are Four Times the hardness of rubies and sapphires.

One of the reasons why Mr De Beers says, Diamonds-are-Forever, is because diamonds are the hardest gemstones on the Mohs' Scale!

Original Mohs' Scale

I was talking to my geologist friend about Friedrich Mohs and the relative and absolute hardness scale and he very kindly told me a little rhyme he learnt at university, to help him remember the order of the Mohs Scale of hardness.

Mohs Hardness Chart

It goes like this:

Two Girls Coming From Alaska On Quick Train Carrying Diamonds

1. Talc - can be scratched with fingernail
2. Gypsum - can be scratched with fingernail
3. Calcite - can be scratched with fingernail
4. Fluorite - easily scratched with knife
5. Apatite - can be scratched with knife
6. Orthoclase - can be scratched with steel file
7. Quartz - scratches window glass
8. Topaz
9. Corundum (ruby, sapphire)
10. Diamond

Applying the Mohs' Scale

When you know about the Mohs relative hardness of gemstones, you can apply this knowledge in properly caring for your jewelry and storing your jewelry.

The luster of gemstones of the Mohs' hardness below 7 can be damaged by Dust. Yes, dust! Jewelry, gemstones, pearls, and antique cameos are allergic to dust. Dust contains tiny particles of Quartz which is Mohs' hardness 7 and is the number 1 enemy of jewelry and gemstones.

Through the scratching of this Quartz Dust, the stones become dull over the course of time. Such stones below Mohs' hardness 7 must be carefully handled when being worn and stored.

These stones should never be stored with gemstones above Mohs' hardness 7 as they will scratch them and always store these gemstones in a dust-free environment.

Have You Seen the Jewel of the Month Yet?

Reference:

Schumann, W., Gemstones of the World, Newly Revised & Expanded Third Edition, Sterling Publishing Co., Inc. New York.

Photo Credit: IN-VSEE consortium of university and industry scientists and engineers

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