Friday, November 09, 2007

Feldspar Gemstones

By far the most abundant mineral group on earth is the feldspars. Yet, when you think of gemstones you don’t associate them with feldspars. However, the feldspar family produces some pretty amazing gems.

The feldspar family is composed silicates (Si2O4) of potassium (K), sodium (Na), and calcium (Ca) where the sodium replaces the potassium and the calcium replaces the sodium in various amounts to create some very common rocks and occasionally, gemstones.

Imagine a triangle ▲ where at the top of point you have pure potassium silicate which is the mineral orthoclase. Most orthoclase is white to fleshy in color and boring. Under special conditions it can form a very rare gemstone from citrine to honey in color and be as transparent as glass.

Now moving down the left side of the triangle toward the bottom left corner we add a little sodium to get sanidine, one of the rarest of the feldspars. Most of the time sanidine is just white and opaque like the crystals from Tooele. Given the right conditions it can form a smoky quartz look-a-like.

Add enough sodium now to make it a 50:50 mix and you get moonstone. Moonstone is one of the gems that have many faces. It can be orange, yellow, green, red, gray, brown, and black. But the most sought after is the blue. When you get a blue flash across a semi-transparent stone it is just amazing. Even more beautiful is when the blue is mixed with orange, yellow, or red. Then you see a rainbow dancing within the stone. This is one of the most popular gemstones in the world. It is said to bring young maidens great luck.

Once you have replaced all the potassium with sodium you have microcline, a.k.a. amazonite. This forms opaque stones that are robin-egg blue to deep emerald green.

Now we move across the bottom of the triangle from left to right replacing the sodium with calcium.

Oligoclase is a rare and visually stimulating gemstone. It forms various shades of greens from mint green to pastel green like tourmalines. It can also form shades of yellow, tan, and brown.

With a little more calcium you get sunstone, a very popular gemstone. Our Utah sunstone is fun to collect but it doesn’t really turn out a good gemstone. The material from Oregon however, is the finest in the world. It forms blood red to pastel reds and green, tan, yellow, brown, and black. The highest quality is the red with inclusions of copper flakes that make the stone shimmer or glitter as it moves in the light. I particularly like the ones with red and green together, they remind me of Christmas. This sunstone is probably the most valuable feldspar on the market.

With a 50:50 mix of calcium and sodium you get labradorite. Calcium and sodium molecules are round and large so when they mix there is there is a lot of space between them. This space, called interstices, fills with water and creates a prism as the light refracts off of it. This phenomenon is called labradorescents. We see the colors of a rainbow--yellows, blues, greens, oranges, reds, and violets. They are often very vivid and striking, making this mineral a favorite among mineral collectors, gemstone collectors, jewelry wearers, and just about anybody who sees it. Though named for Labrador, Canada where it was first discovered, the best material comes from Madagascar. Labradorite is often called spectralite or galaxite.

Moving to almost pure calcium you get bytownite. It is among the most rare of gemstones and a favorite with collectors. It has a warm glowing yellow to amber color.

We have a few of these feldspars in stock. We have some moonstone cabs of different colors, sunstone, labradorite, amazonite, etc.

Adrienne is updating the minerals on the website about once a week. This week she should have about 50 more specimens on including guitar picks custom made by Alston and gemstones.

CLICK HERE to check it out! 

Rockpick Legend Co.
1017 S Main Street
Salt Lake City, Utah 84111

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