If you've ever had the pleasure of holding labradorite, moonstone, sunstone, or amazonite, then you might be more familiar with the feldspar family than you think! The feldspar mineral group is one of the most abundantly occurring mineral groups due to it's ability to form within a wide variety of geological environments, such as in granite, clay, and sand. Feldspar is a member of the silicate family, an aluminum rich variety.
Within the feldspar family, we have highlighted two distinct classifications: plagioclase and alkali. Plagioclase is the sodium rich variety, and alkali feldspars (sometimes referred to as k-feldspar or orthoclase) are the potassium rich variety.
Because the feldspar group branches off so much, we decided to focus on the most popular varieties of feldspar -- which are also available in our store!
Labradorite is a plagioclase feldspar. First discovered in Labrador, Canada, labradorite is known for it's striking play of colors known as "labradorescence". This results from a structural color effect where light enters the stone and strikes twinning layers within the internal structure. The amount of layers, and what they are composed of, determines how intense the colors will be. Labradorite is often found within gabbro and other mafic igenous rocks.
Moonstone can occur as a plagioclase feldspar or an alkali feldspar. The most commonly known is the plagioclase variety, which is white with a blue to green play of light. This play of light within moonstone is known as adularescence.. The potassium rich variety often occurs in a peachy pastel hue with a floating sheen, giving it a silky or pearly luster.
Sunstone is a transparent variety of feldspar that receive's it's shimmer from inclusions of either copper, hematite, or sometimes goethite. These plate-like inclusions reflect light in a way that causes the sunstone to appear as if it was glittering. This optical effect is known as aventurescence.
Amazonite is a translucent alkali feldspar and quite possibly the most popular in it's group due to it's rich teal colors and interesting crystal structure. When tumbled, amazonite will display a similar adularescence as moonstone.
We hope this gave you an added appreciation for the feldspar mineral group and helped you learn something new! #doitfortheGRAM