All that glitters isn’t diamond, ruby, emerald, or sapphire. Spodumene, for example, has two beautiful gem varieties: kunzite and hiddenite.
Spodumene is related to jadeite and other pyroxenes. It’s the only member of the pyroxene family that contains lithium and the only one found in rocks that are high in silica, aluminum, potassium and oxygen (i.e., felsic).
Rocks called pegmatites are where you’ll find spodumene. Pegmatites crystallize out of underground magma that has a lot of water in it. This magma and water probably have been “sweated out” during the process of metamorphism, which involves intense heat and pressure.
The water and some unusual elements (like lithium) get concentrated in the magma because they aren’t used by the first minerals that form when the melt starts cooling off.
When spodumene finally does form, its crystals can be be many tens of feet long.
Spodumene’s name is from the Greek for “ash-colored.” The mineral actually comes in many colors, depending on chemical impurities. It can also be colorless.
Transparent, colored stones are strongly pleochroic. That is, the color changes depending on the angle you’re looking at it.
Gem cutters try to take advantage of this, but they have to be careful. Spodumene is very splintery and hard to work with.
Manganese (specifically, Mn3+) gives kunzite its unique pink to lilac color.
Kunzite was first identified by George F. Kunz, whom we met earlier this week, and is named after him. It is quite popular both as a gem and a decorative stone.
As of this writing, the Gemval prices listed for a 1-carat kunzite stone range from USD 35.02 (colorless) to USD 79.02 (light purple/slightly grayish).
Major sources for kunzite are Afghanistan, Brazil, Madagascar, Pakistan, Sri Lanka, and the US state of California.
Few people but collectors know about the yellow to green gem hiddenite. It’s a much rarer gem form of spodumene that used to be found only in Alexander County, North Carolina. It now has also been discovered in Brazil and Madagascar.
The green color of hiddenite (which was named after geologist William Earl Hidden), usually comes from chromium, but sometimes vanadium, iron and manganese (specifically, Mn4+) will do it, too.
The current Gemval prices for a 1-carat hiddenite stone range from USD 83.41 (slightly yellow/brownish) to USD 970.97 (medium light green/slightly grayish, untreated).
Kunzite and hiddenite gemstones are often irradiated and then heated to deepen their colors. The colors in both natural and treated gems fades after repeated exposure to heat or bright light.
Spodumene ore is mined for lithium, but its main value comes from its semiprecious kunzite and hiddenite varieties. Kunzite’s pink to lilac color is like no other gem, while the much more rare hiddenite can be yellow to a rich shade of green that rivals emeralds. Both gems are beautiful and a bargain at the jewelry counter compared to the much more expensive precious stones.
- Pyroxene. University of Minnesota
- Spodumene. Amethyst Galleries
- Spodumene. Gemdat
- Spodumene. Mindat
- Hiddenite. Wikipedia
- Lithium. Wikipedia
- Spodumene. Wikipedia
- Front page image source