Check them off as you find them, and keep track of where they come from. This is the easiest mineral to find on Guam. Limestone is made of calcite. It ranges from fine-grained and powdery to coarsely crystalline in rocks such as crystalline limestone and skarn.
Calcite is so soft that it can be scratched by a penny.
Our calcite is mostly white to colorless, but we also have pale yellow, pink, brown, and gray calcite. Calcite fizzes in dilute hydrochloric acid. A variety of microcrystalline quartz, this mineral is abundant around Guam's volcanic rocks. It results from the chemical weathering of basalt and other igneous rocks. Agate, a banded variety of microcrystalline quartz, is also common.