How hard is it? A simple guide to Mohs’ Scale

Gemstones and mineral specimens have many properties.  One that is particularly important for jewelry is hardness.  Why? A stone that is soft should not be used in an unprotected setting or in a piece that is likely to be bumped.

For example, I had a lovely opal ring with four opal cabochons in prong settings.  Not realizing at first how fragile opal can be, I wore the ring regularly.  It didn’t take long before I’d chipped one of the stones.  I was slightly more careful with it but still managed to chip a second stone and lose that first one (as it was loose in its setting).  Fortunately, we were able to match up the opal, cut and polish new cabochons and restore the ring completely.

For stones that are below 7 on the Mohs’ hardness scale, dust can do some damage if rubbed into the stone as quartz particles are fairly common in dust.  To help identify how hard a stone is, there is a “simple hardness tester” that can be used as a guide and to provide an idea of what the various scale values mean along with an example in parenthesis[1]:

  • 1 (talc) and 2 (gypsum): can be scratched with a fingernail
  • 3 (calcite): can be scratched with copper coin
  • 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), 10 (diamond) : no simple test 

I would not recommend actually trying any of the scratch tests on finished stones but rather use the information to help understand what the various Mohs values represent.  Note that the scale is relative, so that the difference between a 4 and 5 on the scale is not the same as the difference between 9 and 10.

[1] Gemstones of the World: Newly Revised & Expanded Fourth Edition by Walter Schumann, p20 (based on the table “Relative and Absolute Hardness Scale”)

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Stars in stones – asterism

Asterism is a term which describes “the effect of light rays forming a star (Latin aster, star)…It is usually created through reflection of light by thin fibrous or needle-like inclusions that lie in various directions.” [1]

Stars in gemstones may have four, six, or (less frequently) twelve rays.  With these stones, the angle of the stone to a light source is important to be able to see the star.  Natural gemstones known to exhibit asterism include:

Star ruby with six-rayed star
Star ruby with six-rayed star. One of the lovely stones in our collection at Dragon Dreams Jewelry, LLC.
  • star sapphire
  • star ruby
  • star diopside
  • star rose quartz
  • star blue quartz
  • star garnet
  • star spinel

[1]  Gemstones of the World: Newly Revised & Expanded Fourth Edition by Walter Schumann, p.52

New treatments for corundum might be bad for your health

In previous posts, we’ve discussed both sapphires and rubies, which are varieties of corundum.  This popular, colorful, and durable gemstone is highly prized.

Corundum is now being diffusion treated with titanium and chromium, where the stone is irradiated to get the colorant to absorb into the outer layer of the stone.  Another treatment, beryllium diffusion, has been common for years.  Stones treated with any of these methods may lose part or all of their color if the stone is damaged or repolished.

It is possible that there are health hazards from these stone treatments.  For example, chromium is toxic and may damage DNA cells. [1]    “There is disturbing evidence that suggests the beryllium treatment poses a health hazard to the workers who process and cut the gemstones and to the merchants who handle them.” [2]

Surprisingly, irradiated gemstones are generally considered safe because of the mandated cooling off period and monitoring requirements.  “NRC [Nuclear Regulatory Commission] requires that the initial distribution of these stones be by a distributor licensed by the NRC. This distributor would conduct radiological surveys of each batch of gemstones to ensure that any residual radioactivity falls below regulatory limits.”  [3]

Sellers in the United States are required by law to disclose all treatments to stones they sell.

 

[1] http://en.wikipedia.org/wiki/Chromium#Precautions

[2] The Jeweler’s Directory of Gemstones by Judith Crowe, p.50

[3] http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/irradiated-gemstones.html

Featured stone: ruby

The Latin ruber, meaning red, is the likely origin of the name ruby.

Prior to the 1800s, there was not a distinction made between red spinel, red garnet, and ruby[1].  As a result, some of the most famous rubies of the world are not actually rubies.  For example, the Black Prince’s Ruby is actually red spinel.   There are also a number of misnomers for ruby[1]:

  • almandine ruby (red garnet)
  • Australian ruby (red garnet)
  • balas ruby (red spinel)
  • Bohemian ruby (red garnet)
  • cape ruby (red garnet)

Chatham ruby, Ramaura ruby, Linde star ruby are all names describing synthetic, flux grown ruby.

Ruby is a variety of corundum which has a purplish-bluish red to yellow-red color (sapphire is used to describe corundum of any other color).  Ruby has a Mohs hardness of 9, making it quite durable and strong.

Clean your ruby jewelry with water mixed with a small amount of mild liquid hand soap with a soft cloth, rinse with water and dry with a soft cloth.  You may want to use a toothbrush to clean under the stone.  While rubies are not particularly light sensitive, all colored stones can fade with prolonged intense exposure to sunlight, so be sure to store your ruby jewelry out of direct light.  As ruby jewelry can last many years, periodically check the prongs and/or settings to be sure the metal is still holding the stone securely in place.

Rubies can have fractures filled with oil, wax, paraffin, glass, or epoxy resin as fillers, reducing the visibility of flaws and cracks within the stone.  When this has been done, the ruby is considered to be composite, reducing the value of the stone although the it will look better to the naked eye as the fractures will be nonreflective[1].   Rubies, like sapphires, can also be heat treated to improve the color.  Most of the rubies we have seen recently in chain jewelry stores have been lab created rather than natural stones.  Sellers are responsible for disclosing all treatments and whether the stone is natural or lab created.

Some of the metaphysical properties associated with ruby include:

  • shields against negative intentions
  • guards against psychic or physical attack
  • helps to be warm, caring toward others
  • reinvigorates and restores energy
  • encourages love, passion, joy, spontaneity, laughter, and courage
  • balances the heart
  • improves motivation

Chakras: root, heart

[1] The Jeweler’s Directory of Gemstones by Judith Crowe, p.50

We have gorgeous ruby jewelry items on our site at www.dragondreamsjewelry.com.

Ruby and Sterling Silver earrings

Featured stone: sapphire

Sapphire is believed to derive its name from the Greek σάπφειρος; sappheiros, meaning ‘blue stone’.  However, there are a variety of possible word origins from Latin, Sanskrit, Hebrew, and other languages.

A 12th century writing by Abbess Hildegard von Bingen includes this use for a sapphire: “Who is dull and would like to be clever, should, in a sober state, frequently lick with the tongue on a sapphire, because the gemstone’s warmth and power, combined with the saliva’s moisture, will expel the harmful juices that affect the intellect. Thus the man will attain a good intellect.”

Sapphire is a variety of corundum which comes in a variety of colors, including pink, yellow, green, purple, blue, colorless (virtually any color except ruby, another variety of corundum which has a purplish-bluish red to yellow-red color.)  Sapphire has a Mohs hardness of 9, making it quite durable and strong.

Clean your sapphire jewelry with water mixed with a small amount of mild liquid hand soap with a soft cloth, rinse with water and dry with a soft cloth.  You may want to use a toothbrush to clean under the stone.  While sapphires are not particularly light sensitive, all colored stones can fade with prolonged intense exposure to sunlight, so be sure to store your sapphire jewelry out of direct light.  As sapphire jewelry can last many years, periodically check the prongs and/or settings to be sure the metal is still holding the stone securely in place.

Because these beautiful stones are durable and colorful, there are many synthetics and imitations on the market.  Heat treatment of sapphire has been a common practice since the 1960s [1].  Most of the sapphires we have seen recently in chain jewelry stores have been lab created rather than natural stones.  As always, be sure to ask your seller.

Some of the metaphysical properties associated with sapphire include:

  • bring clarity and clear perception
  • assist communication, including with the spirit realms
  • release mental tension
  • enhance creative expression and intuition
  • promote fairness and loyalty
  • protection during astral travel

Chakras (by color):
White, purple – Crown chakra
Blue – Third Eye and throat chakra
Padparadscha, Yellow – Solar plexus chakra
Green – Heart chakra

[1] The Jeweler’s Directory of Gemstones by Judith Crowe, p.48

We have many lovely sapphire jewelry items on our site at www.dragondreamsjewelry.com.

Sapphire in Sterling Silver