A rhombahedron of calcite
Click on image for full size
Find out how to identify minerals (...and learn what shape, luster, color, streak, hardness, cleavage and fracture are all about!)
Meet some other nonsilicate minerals!
Try the calcite optical illusion!
Calcite is typically found in the sedimentary rock called limestone. Calcite is also in marble, a metamorphic rock, which forms when limestone is put under strong heat and pressure.
Calcite crystals have three planes of cleavage. This gives perfect crystals of calcite, like in the picture at the left, a rhombahedron shape.
Everyone's favorite way of identifying calcite is the acid test. When you place a drop of weak acid, such as vinegar, on calcite, it will bubble. This happens because a reaction causes a little bit of the calcite to break down, releasing carbon dioxide gas, making the bubbles.
Sometimes rocks that are made primarily of calcite are dissolved away by acidic groundwater making caves underground. Stalactites and stalagmites form in cave when calcite comes out of the groundwater.
- Shape: Trigonal (rhombahedral shape)
- Luster: Glassy to resinous. Large samples often look dull.
- Color: Usually white or colorless but sometimes is found in light pastel colors.
- Streak: White
- Hardness: 2.5 to 3 on Mohs Hardness Scale
- Cleavage: Perfect in three directions
- Fracture: Conchoidal
Last modified April 15, 2003 by Lisa Gardiner.
Shop Windows to the Universe Science Store!
The Fall 2010 issue of The Earth Scientist
, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!
You might also be interested in:
The sediment in an organic sedimentary rock is made of fossils! The hard parts of animals, such as bones and shells, can become cemented together over time to make rock. Usually the bones and shells are...more
Unlike most other sedimentary rocks, chemical rocks are not made of pieces of sediment. Instead, they have mineral crystals made from elements that are dissolved in water. The water in the oceans, lakes,...more
Making concrete releases carbon dioxide (CO2), a greenhouse gas, into the atmosphere. The carbon dioxide from concrete, combined with greenhouse gases from many other sources, is causing Earth to warm....more
Spotting minerals is fun! There are many different types of minerals, each with a different name and a special set of characteristics. So, if you find a mineral that you do not recognize, you can use...more
Quartz is one of the most common mineral in Earth’s crust! Silica (Si) and Oxygen (O) are the only elements within pure quartz. If a cooling magma has silica leftover after feldspars form, quartz is likely...more
Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which...more
Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous...more