Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium. It is rare and valuable in its finer grades and has been prized as a gemstone and ornamental stone for thousands of years owing to its unique hue. In recent times Turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the gemstone marketplace. The substance has been known by many names, but the word Turquoise was derived around the 16th century from the French language 'turquie', for a Central Asian material which was a very early imported through Turkey from Persia. Today, Persian and certain southwestern United States Turquoise, especially Sleeping Beauty, commend some of the highest prices paid for this gemstone. Many times on the edges of the Turquoise fields, other minerals and stones become interwined into the Turquoise or Turquoise pieces are encapsulated into the surrounding rock, thus creating unique and interesting patterns.
Ivoryite is a great substitute for ivory. It is a sedimentary precipitate of magnesium, calcium and silica. It is 5 to 5-1/2 on the Moh's scale, which makes it slightly harder than ivory. Ivoryite can be worked with metal tools, but cuts effortlessly with diamond tools. Polishes well with diamond, tin oxide, cerium oxide or white rouge. Excellent material for inlay, cabochons and small carvings. Do not confuse Ivoryite with Ivorite, whic is a black tektite material from Africa. The majority of Ivoryite currenly comes from the western United States, especially Colorado and California.
Black Agate (Onyx) which is truely a died black Agate, is more common and perhaps the most famous variety, but not as common as natural Onyx. Onyx is a crypyocrystalline form of Quartz. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). A picture of a true Black Onyx specimum is seen below. True specimens of Onyx contain bands of colors of white, tan, and brown. As stated, the pure black form which most people know as Onyx, is not a naturally occuring variety. Black Agate or poorly colored Onyx is heated and dyed black to come up with the pure black form so well liked within the jewelry industry.