Named for its calcium content, calcite is one of Earth's more abundant minerals-- you've probably seen it many times and not known exactly what it was. It is found in granite and limestone veins and streaks as well as other rocks used in driveways and roads. Gem-quality calcite, however, takes on a quite different look. You may have seen colorless calcite crystals used as examples for double image refraction, but it also forms as white, gray, yellow, pink and green gems. Material is often faceted or polished en cabochon, or carved into ornamental objects.