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The Mohs Hardness Scale

What is it?


The Mohs Hardness Scale is a tool used by geologists to help identify unknown minerals. The Mohs scale works by determining the relative scratch resistance, or hardness of a mineral, with minerals oh a higher hardness having the ability to scratch minerals of a lower hardness.

Essentially, every mineral falls somewhere along a scale from 1 to 10, with 1 being a poorly scratch resistant mineral (low hardness), and 10 being highly scratch resistant (high hardness).


History


The Mohs Hardness Scale was officially introduced in 1822 by Friedrich Mohs in his book the "Treatise of Mineralogy" (also known as "The Natural History of the Mineral Kingdom"). However, the ideas behind the Mohs Hardness Scale, using the scratch resistance of different minerals to determine their hardness has been used since antiquity (see "On Stones" by Theophrastus, 300 B.C. and "Naturalis Historia" by Pliny the Elder in 77 A.D.).


Minerals


The Mohs Hardness Scale typically uses 10 relatively common minerals that are representative of each integer along the Mohs scale. These are as follows:


  1. Talc = 1

  2. Gypsum = 2

  3. Calcite = 3

  4. Fluorite = 4

  5. Apatite = 5

  6. Feldspar =6

  7. Quartz = 7

  8. Topaz = 8

  9. Corundum = 9

  10. Diamond = 10

These minerals are known as index minerals, meaning the vast majority of raw specimens for each listed mineral will have a known hardness. This known hardness can be used to help identify an approximate hardness for an unknown mineral.


A relative hardness can also be identified using common household objects. These objects can be scratched against the unknown mineral and have a listed hardness below:


  1. Fingernail (2 - 2.5)

  2. Copper Sheet (3)

  3. Nail (4 - 7)

  4. Glass (4 - 7)

  5. Steel File (5 - 6.5)

  6. Knife Blade (5 - 6.5)

  7. Streak Plate (5 - 7)

  8. Quartz (7)


Testing Procedure


  • Locate a smooth, unscratched surface for testing, and with one hand, hold unknown mineral firmly against a table top so that the surface to be tested is exposed and accessible.


  • Hold one of the known hardness specimens (as listed above) in the other hand and place a point of that specimen against the selected flat surface of the unknown specimen. Firmly press the point of the standard specimen against the unknown mineral, and with firm pressure, drag the point of the standard specimen across the surface of the unknown specimen.


  • Examine the surface of the unknown mineral and brush away any mineral fragments or powder that was produced. Is there a visible scratch? Be careful to not mistake mineral powder or residue with a scratch. A scratch will be a distinct groove cut in the mineral surface, not a mark on the surface that wipes away.


  • Conduct the test a second time, and then repeat procedure with a different known hardness specimen.

Why do we need to know about the Mohs Scale?


The Mohs scale is an incredibly important tool for all rockhounding enthusiasts, crystal buyers and sellers alike.

With so many artificial stones flooding the industry, seller ignorance, and the rise of trends such as crystal confetti, understanding the interaction between different minerals and their relative hardness, as well as being able to quickly identify stones through their expected hardness has never been more important for both buyer and seller.


Crystal Confetti?


Crystal Confetti is just one of several recent crystal trends stemming from TikTok and various social media outlets. The aim behind crystal confetti is to provide a scoop of various tumble, raw, carved and polished crystals, often related to a holistic theme (i.e. success, calming, healing). Often, sellers hold very little knowledge or regard to the variety of crystals within the confetti, and so crystals all along the Mohs Scale are added and mixed together. This would not be an issue, if the more delicate minerals were packaged accordingly. Unfortunately they often aren't, and when the crystals reach the buyer, many are damaged beyond use.

I personally love the idea of crystal confetti, when done right. Typically sticking to a range from Mohs 5 to Mohs 7.5 is ideal, and to simply wrap up everything carved/polished, or anything higher or lower on the Mohs Scale. There are several minerals within this range that fit with almost all holistic themes, and the risk of severe damage to the crystals is significantly lower.


Thanks for reading!



Further Reading


https://geology.com/minerals/mohs-hardness-scale.shtml

http://www.minsocam.org/msa/collectors_corner/article/mohs.htm

https://flexiblelearning.auckland.ac.nz/rocks_minerals/minerals/hardness.html




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