Mohs Hardness Scale

By Emily on April 22, 2012 at 12:37 pm

The Mohs scale of mineral hardness was developed by German mineralogist, Frederich Mohs in 1812. The scale is used to characterize stones relative hardness and scratch resistance.  The method of determining hardness is by testing the ability of a harder stone to scratch a softer stone. The scale ranges from 1 to 10 with 1 being the softest and 10 being the hardest.  One thing to keep in mind is that the scale is purely an ordinal scale. That being said, sapphires are twice as hard as topaz and diamonds are four times as hard as sapphires, despite their numbers on the Mohs hardness scale.

A mineral’s hardness is its ability to resist scratches. A mineral’s toughness is its ability to resist being fractured.

Below is a list of some of the most common gemstones we work with, including their ranking on the Mohs hardness scale as well as its toughness.

Gemstone Mohs Hardness Scale Toughness*
Diamond 10 Good
Sapphire 9 Usually excellent
Ruby 9 Usually excellent
Alexandrite 8.5 Excellent
Spinel 8 Good
Aquamarine 7.5 Good
Emerald 7.5 Poor to good
Amethyst 7 Good
Citrine 7 Good
Malaya Garnet 7 Fair to good
Rose Quartz 7 Good
Smoky Quartz 7 Good
Tourmaline 7 Fair
Peridot 6.5 Fair to good
Moonstone 6 Poor
Tanzanite 6 Fair to poor
Opal 5 Very poor to fair
Turquoise 5 Generally fair
Pearl 2.5 Usually good

*Toughness scale: poor, fair, good, excellent

If you are looking for a durable stone, diamonds, sapphires and rubies are the best options.

Comments (2)

  1. Mohs Scale is not a absolute scale. It’s rather a relative scale which is based on principle that if a material A is able to scratch material B then A is relatively harder than B. For measurement of absolute hardness, Sclerometer is used.

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