What are the Inclusions in Sunstone?

Sunstone is a type of feldspar mineral that displays an optical phenomenon called schiller. This schiller effect manifests as metallic specks or glints of light that appear to move or shimmer as the stone is viewed from different angles. These sparkling inclusions are responsible for the prized visual appeal of sunstone.

The most common mineral inclusions found in sunstone are tiny plates of copper or iron oxides such as hematite and goethite. The plate-like shape of these metallic inclusion causes them to diffract and reflect light in a way that produces the schiller effect for which sunstone is so famous. When oriented parallel to the surface of the stone, the oxide plates act like tiny mirrors that catch and reflect light. Slight movement or changes in lighting angle alter how the plates reflect light, creating an eye-catching sparkle.

While copper and iron oxide plates dominate, sunstone can also harbor inclusions of other minerals that add to its beauty. Rutile, a metallic form of titanium oxide, sometimes occurs as fine acicular (needle-like) crystals within sunstone. When present, rutile inclusions diffract light into stunning displays of red, blue, and golden flashes. Chlorite, biotite, and hematite may also appear in sunstone as thin, feather-like crystals oriented in radial patterns. Calcite is another potential inclusion in sunstone, forming small crystal aggregates that add sparkle.

Along with its metallic schiller-producing inclusions, some sunstone exhibits dramatic color banding due to trace elements present during its formation. Bands of color can range from clear to pale yellow, deep crimson, and various shades of orange and red. Variations in mineral composition during sunstone’s creation can produce striking color gradients and patterns. The most valuable and beautiful sunstones exhibit a strong schiller effect against a background of vibrant color banding.

Sunstone forms through the slow cooling of molten silicate material containing various metal oxides in solution. As the melt cools, crystals of feldspar form while metallic compounds cluster into plates, needles, and crystal shapes. The final sunstone reveals this intricate mingling of feldspar and metallic minerals as intriguing visual features. expert cutters orient sunstone to maximize the face-up view of these special inclusions.

Part of sunstone’s allure lies in the many possible inclusion and color patterns produced through natural geologic processes. The random natural designs make every sunstone unique. From fiery copper schiller to muted grey flashes, part of the beauty of sunstone is the variety of natural inclusions that can occur. Generally speaking, the most desirable sunstones exhibit bright schiller and lively coloration caused by complex inclusions.