Calcite, or calcium
is one of the world's most common minerals. It's the main
of both limestone and marble, rocks used as dimension stones and in
mortar for thousands of years. (Limestone blocks were the
construction material used in many of the ancient pyramids of Egypt and
When dissolved in water, Calcite can be precipitated from drips in
limestone caves as stalactites
Most Calcite forms in masses and aggregates, but good crystals do form
in hydrothermal veins, alpine fissures, and pockets in basalts and
is best recognized by its relatively low Mohs hardness (3), its
vitreous luster, and its high
reactivity with even weak acids like vinegar.
It's found in a rainbow assortment of colors, including yellow, brown,
orange, pink, red, purple, blue, green, gray, black, white, and
colorless. You can see another type, Dogtooth Calcite, here.
The Orange Calcite
specimens on this page are from Mexico,
and look just like juicy pieces of real oranges!.