Is Sunstone a Labradorite?

Sunstone and labradorite are two visually stunning feldspar minerals often mistaken for one another due to their flashy, iridescent displays. While similar in appearance, they are actually quite distinct minerals with their own unique properties and origins.

Labradorite is a plagioclase feldspar containing sodium and calcium that exhibits an iridescent optical effect known as labradorescence. This flashy play of color is caused by light interacting with lamellar twinning in the crystal structure. The labradorescence can display all the colors of the rainbow in shimmering blues, greens, yellows, oranges, and reds. High quality specimens from Labrador, Canada (the mineral’s namesake) display these colors very vividly.

Sunstone is a variety of oligoclase feldspar that contains hematite or other minerals that produce its signature sparkling glints of light. The glittering reflections of light are typically red, orange, and green in color. The sparkles are caused by platelet inclusions of copper that reflect light within the stone. Different minerals like hematite, goethite, or pyrite can also produce the sparkles in sunstone. The highest quality sunstones come from Oregon, USA and display abundant flashes of red and green light.

While labradorite and sunstone can both display stunning flashes of iridescent color, their optical effects have different causes and appear visually distinct. Labradorite shows a smooth schiller effect across the surface when moved, while sunstone has clearly defined sparkles that look like glitter. The body color also differs, with labradorite ranging from dark gray to blue and light green. Sunstone has a distinctive warm golden orange to brown or red body color.

In terms of composition, labradorite is a sodium calcium plagioclase feldspar that falls between the end members of albite and anorthite. It typically contains 50-70% anorthite in its structure. Sunstone is primarily composed of oligoclase, a sodium calcium feldspar on the plagioclase series that contains 70-90% albite. So while both are technically feldspars, sunstone has more sodium and less calcium than labradorite.

The gemstone varieties also form in different geologic environments. Labradorite is typically found in mafic igneous rocks like basalt and gabbro, often near metamorphic aureoles. Some deposits are in pegmatites related to anorthosite intrusions. Sunstone forms in intermediate to silica-rich volcanic rocks that contain the necessary minerals that produce its sparkle. Oregon’s sunstone deposits are associated with lava flows that host copper and iron sulfide mineralization.

In summary, while these two feldspars can appear similar at first glance, sunstone and labradorite are actually quite distinct in their optical effects, compositions, colors, and geological origins. Labradorite is a plagioclase feldspar that shows iridescent schiller, while sunstone is an oligoclase feldspar displaying sparkly inclusions. They make unique additions to any mineral collection and showcase the stunning effects of light interaction with the crystal structure of minerals. So while they may sometimes be confused, sunstone does not equate to labradorite. They are dazzling minerals in their own right.