Gem Focus June 2020: Kunzite: a rosy spodumene with an American name
*Gem Focus & Market Pulse (Free Subscriber)Spodumene is almost exclusively a pegmatitic mineral of the pyroxene group that forms in monoclinic system with a chemical formula of LiAlSi2O6. Its hardness is 6.5 to 7 on the Mohs’ scale and displays perfect prismatic cleavage. Transparent and colored varieties show strong pleochroism. Strangely, the name spodumene means “ash-colored” in Greek referring to the dull and colorless examples when it was first named in the second half of the 19th century.
In 1879, an exciting green and transparent variety of spodumene was discovered. It was named hiddenite after its type locality Hidden, North Carolina. It is considered to be the rarest of spodumene varieties and colored by chromium. Gemologists must understand that not all green spodumene from Hidden, NC is hiddenite. This is a misleading practice in the gem market which is sometimes extended to other green and yellow spodumenes from other localities too. A true chromium colored hiddenite with a saturated green color is extremely rare. There is also a yellow
variety called triphane.
George Fredrick Kunz, the legendary American mineralogist-gemologist must have been very excited when he first discovered a pink variety of spodumene as it had been known only in colorless and green. He and Charles Baskerville first published their findings of pink spodumene from Pala, California in 1903. Almost a year later, Mr. Baskerville named this variety as “Kunzite” in honor of G.F. Kunz. In his famous book of “The Curious Lore of Precious Stones,” Mr. Kunz humbly suggests an alternative birthstone’s list for Americans in 1913. He writes; “As it might seem appropriate that one born in the United States should wear a gem from among those which our country furnishes, the following list was sometime since prepared by the writer, not in any sense as a substitute for the real birth-stones, but as possible accessory gems (when they are not identical), gems which might be worn from a spirit of patriotism.” In this list, kunzite is marked for September and listed as found in California.
Kunzite’s subtle rosy color is in pink to purplish pink range and caused by manganese. Most stones display very light tones so it is common to see them cut with deep pavilions. Since the color is so light, small stones look almost colorless. A nicely colored faceted kunzite with correct orientation would display a medium purplish pink with an eye visible pleochroism. However, kunzite is like a delicate rose. Not only does its perfect cleavage pose a durability issue but also its color may fade away once it is exposed to daylight, more specifically ultraviolet light. If the natural pink of kunzite is bleached via sunlight exposure, it may be restored by irradiation, followed by heating at low temperatures of 100°C to 200°C to remove the green and sometimes brown colors. It is also known that such low temperatures are used to draw out the bluish tinge to produce more pink stones. Unfortunately, the irradiation of kunzite for color treatment cannot be detected.
Major gem quality producing localities include Brazil, Afghanistan, Madagascar alongside California. One of the largest faceted kunzites of the world is in the National Gem Collection of the Smithsonian Institute. This 880 carat heart shaped gem is from Brazil. Afghanistan is known to produce fairly large kunzite crystals too. In fact, a well-formed gemmy kunzite crystal attached to the matrix may be worth more as mineral specimen than a faceted stone as long as the locality is documented accurately.
Kunzite is a fairly affordable gemstone and needs careful setting due to its durability issues. While stones over 10 carat sizes might be sold around $150 per carat in extra fine category, the similar weights in commercial range can go as low as $8 per carat at wholesale level. Since the treatment is not detectable, there is no price difference can be applied. Kunzite is not known to be synthetically produced either. Any simulant can be separated through conventional gem testing methods easily.