There are several scales that are used by Gemologists to determine hardness, durability or the scratch resistance of gemstones.  The one that is most widely recognized is the Moh scale, which is really a table that indicates the scratch resistance of gemstones.   A German minerologist by the name of Friedrich Moh developed a scale in 1822 to compare the scratch resistance of gemstones.  It has become universally known as Moh's scale, with Diamond being a 10 or the most scratch resistant to Talc at a 1, which is the least scratch resistant.

I bring this up because most gemstones are enhanced in one way or another to increase durability, reduce scratch resistance or improve the look of the stone, or to even create a new look.  For example, Carnelian can be heat-treated to produce that dark, rich reddish-orange color as found in some of the beads pictured below.
 
 
Generally, high scratch resistance is desirable for gemstones, and a Moh's hardness of 7 or higher is important. The principal reason is that a common cause of abrasion is sand, which is silica grit (quartz), and is commonly present in dust. Stones which are softer than quartz are not suitable for everyday use as facetted jewelry gemstones, particularly in rings.  Some gems, such as Pearls, Coral, Turquoise, Lapis Lazuli, Amber, and Opal are quite soft, but are usually polished into cabochons or beads, rather than facetted, and therefore do not show scratches so easily. All these gemstones have been successfully used in jewelry for many centuries.

Most gemstones used in jewelry have been treated to improve their appearance. Treated gemstones can be a good choice when you know what you are buying and pay a price that reflects a stone's true quality.  There are Industry Standards that indicate the type of enhancement and whether they are permanent or not.  You’ll probably come across the phrase “enhanced as per Industry Standards”.  So don’t be worried if the gemstones in your piece of jewelry have been enhanced.  Sometimes enhancement can make a gemstone more valuable.  If you're interested in more detail on the various enhancements for gemstones then you can read my blog.  You can find the link on My About Me page .
 
Two of the gemstones that I would like to discuss that are usually enhanced are Turquoise (a mineral gemstone) and Coral (an organic gemstone) which are consistently at the top of the list for the most popular gemstones and they are always in fashion.  Another term that you will hear is Stabilization, or that a stone has been stabilized and it is usually used with stones that are less than a 7 of the Moh’s scale.  This is especially true with Turquoise and Coral.
 

Turquoise is an opaque, light to dark blue or blue-green gem. It can also have a distinct yellow or limey green tone as seen in Chinese Turquoise.  The finest color is an intense blue. Turquoise may contain narrow veins of other materials either isolated or as a network. They are usually black, brown, or yellowish-brown in color. Known as the matrix, these veins of color are sometimes in the form of an intricate pattern, called a spider web.  The stone ranges from soft/somewhat porous to hard.  The hard Turquoise is compact and wears well and is never enhanced and is found in the most expensive pieces of Turquoise jewelry.
 
Turquoise is mined all over the world, but a great deal comes from the West and Southwest United States.  Natural turquoise is often too unstable to be used in jewelry so it is often subjected to a stabilizing treatment that soaks in various binders such as polymers to add strength. This is a common trade practice and in my opinion should not prevent a person from buying specimens or jewelry containing stabilized Turquoise. Be aware of simulated Turquoise, and so-called reconstituted Turquoise. Simulated Turquoise is generally the mineral Howelite which is dyed to emulate real Turquoise.  
 
                             
You can see from the pictures that Howelite has a similar matrix as Turquoise and once dyed it’s difficult to distinguish from natural turquoise if you’re not familiar with the stone.  Personally, I purchase my stock from Dealers that mark very clearly whether a product has been enhanced and they follow the Industry Standard Guide faithfully.  I never use dyed Howelite in my jewelry.  When in doubt, ask!
 
Reconstituted Turquoise is crushed up Turquoise that has a binder applied, then reformed in to blocks which are cut in to gemstone shapes of carved in to figurines etc. The dealer should tell you if you are buying reconstituted Turquoise, it should not cost as much as natural or natural stabilized items.  This type of Turquoise can still make lovely pieces of jewelry at a much more affordable price.  Even dyed Howelite can make some fun and fashionable jewelry…just know what you’re getting.
 
Special care is required for Turquoise regardless of whether or not it is enhanced. A porous gem, Turquoise can absorb anything it touches. Avoid contact with cosmetics, perfumes, skin oil, acids, and other chemicals. Avoid dehydrating it or exposing it to heat. Your jeweler will tell you how to best care for your natural gemstone.
 
White is the most common color in Coral, but a variety of other shades can be found, including pink, orange, red, and black. The rarest color is a deep red.  Coral is commonly enhanced to improve its color and durability. White coral is bleached. Pink coral is permeated with a colorless wax and orange coral is stabilized with a polymer. Black coral is sometimes bleached to create gold coral, although gold can be a natural color of coral as well. Occasionally, red coral is dyed to deepen or to make its color more uniform. All commonly used forms of coral enhancement are stable.
 
There is an ecological concern regarding coral and a lot of the coral reefs are dying off due to pollution, changes in water temperature and poaching.  To combat this concern all coral reefs are protected by various governments and coral sea farms have been created for Coral Reef Rehabilitation and Integrative Biological Research, especially in the South Seas and Australia. There is apparently still enough supply, either from new sources or stockpiled inventory, to meet demand, whether for precious red coral from the Mediterranean Sea, dyed Tibetan coral, or pink coral from the Pacific.  However, the coral industry is bracing for an eventual worldwide shortage. The availability of new coral is dwindling as underwater supplies are depleted. Japan has already imposed strict quotas on coral divers, while Italian divers must dive deeper and deeper to get new red coral. Hopefully the coral sea farms will be a new source of coral in the future, just as pearl farms have become.
 
Special care is required for Coral regardless of whether or not it is enhanced. A soft and porous gem, coral scratches and abrades easily and chlorine, alcohol, ammonia, nail polish remover, and other chemicals can damage it. Remove coral rings when washing and moisturizing your hands. Avoid exposing your coral to extreme temperatures. Your jeweler will tell you how to best care for coral.
 
And of course, Coral and Turquoise look stunning together when combined in jewelry.
 
Persons wearing Turquoise jewelry must avoid contact with soap and grease and harsh chemicals since this gemstone is softer than others. Storing turquoise jewelry with other harder gemstones may cause scratches against it. Exposure to high heat or perfumes and oils can affect the turquoise stones. Use warm sudsy water to clean your turquoise jewelry and wipe it dry with a soft cloth.
 
Coral Jewelry does not need high maintenance. The gem is fragile and more brittle than other gems. It measures only 3.5 on the Moh’s scale and the splendor of the coral will diminish if not taken care of. Like Pearls, Turquoise, some corals can be porous - these gems will get damaged if immersed in water for too long. Take care not to use too much water while wearing coral bracelets or rings. The water may also dull the polish of the coral making it look lackluster and unattractive. If you plan to go swimming, remove your Jewelry before diving in. The chlorine present in the water can cause the corals to spoil.
 
Store your Corals separately. Buy separate pouches for the Corals, so they do not get scratched. Other stones, which measure more than 5 on the Moh’s scale, can leave scratches on your Coral.
 
As with Turquoise, harsh cosmetic products can also harm your Corals. Use perfumes and sprays before wearing your jewelry as the chemicals present in sprays can damage the Corals. Do not use soap and water or any other detergents to clean corals. If you plan to buy a professional cleaner, check if it is coral friendly. The best way to clean coral is to just wipe it with a soft damp cloth after you have worn it. If your corals do get scratched despite care, take it to the jeweler for a polish; it will look as good as new.