Labradorite and Spectrolite
Bill Long 11/03/04
A Brilliant Array of Colors
One of the things you have to admire about the study of the natural world is the classification system. Everything has its place, even if all of our categories are not crystal clear. For example, there are ten classes of minerals, one of which is called "Organics," even though a mineral is defined as something that is inorganic. But, by and large, it is a great way of dividing and defining the world. Sometimes it even leads to divining that same world.
So, the largest class of minerals are silicates, and one of the subclasses of silicates is tectosilicates, and feldspar is one of the varieties of tectosilicates. Nearly 60% of the earth's surface is composed of feldspar, so it repays some careful attention. Feldspar is used commercially in pottery, tile and glass but can also be a gemstone. There are around twenty varieties of feldspar, with the leading varieties being amazonite, moonstone, orthoclase, labradorite, spectrolite and sunstone. Sodium, aluminum and silica combine with either calcium or potassium in differing amounts to form feldspar. For example, sunstone and labradorite are "calcosodic" feldspars while spectrolite is a "sodopotassic" feldspar.
One of varieties of feldspar is red labradorite or sunstone. I mention this variety first because, as one source has it, "the premier U.S. gem-quality feldspar is mined in Oregon [my home state]. Large quantities of gem-quality labradorite, most of it water-clear, straw yellow or yellow sunstone, has been produced from deposits in southeastern Oregon for many years." This brand of labradorite contains millions of small copper platelets reflecting the sunlight in a golden-red play of color known as schiller. In 1988 deposits of other colors of sunstone/labradorite were found in another Oregon mine (vivid and velvety-red as well as other colors). However, sunstone has been known since antiquity, and it was used by the Vikings as a directional indicator because of the brilliant metallic reflection of the hematite platelets. Contemporary wearers believe that sunstone helps alleviate stress.
Distinguishing itself from sunstone is a gray or colorless to yellow feldspar, called labradorite, containing inclusions of other materials that produce a variety of visual effects. The OED says that it was first named Labradorstein in 1780 by Verner because it came from Labrador and "shows a brilliant variety of color when turned in the light." So special are the blue, green or pink colors displayed when polished that the distinctive play of colors is known as labradorescence. These optical effects are caused by the presence of "minute laminae" of certain minerals in the crystal and arranged parallel to the surface of the stone.
To introduce more terminology, labradorite is one of six plagioclase feldspars. The plagioclase feldspars are arranged from albite, which contains 100% of sodium and no calcium, to anorthite, containing 100% of calcium and no sodium. Labradorite is closer to anorthite, with a 30% sodium and 70% calcium proportion.
Spectrolite was only discovered in 1940 when the Finns were digging an Eastern wall for defensive purposes against the Russians. The Finnish mineralogist Laitakari discovered it and thought it was labradorite, but then because of the brilliant shimmers that even exceeded those of labradorite, concluded that it was a different stone, though of the feldspar family , and coined the term spectrolite for it. Even more rainbow colors than that of labradorite are found in spectrolite. The stunning variety and beauty can be seen on p. 113 of The Color Treasury of Gemstones. A captive rainbow of colors brilliantly shines forth from the spectrolite.
Reflection on the nature of the colors and light that comes forth from gens makes me wonder about the bewildering number of terms used to describe this light. The next essay will introduce most of these terms.
Copyright © 2004-2010 William R. Long