Rocks and Minerals

<---TRIGONAL, minimum symmetry one 3-fold axis.
Examples are calcite, rose quartz and tourmaline



<---TRICLINIC, minimum symmetry none. Examples are sunstone, turquoise and chalcanthite.



<---TETRAGONAL, minimum symmetry one 4-fold axis. Examples are zircon, calomel and wulfenite.


<---ORTHORHOMBIC, minimum symmetry three 2-fold axes. Examples are barytes, alexandrite and olivine



<---MONOCLINIC, minimum symmetry one 2-fold axis. Examples are malachite, orthoclase and moonstone



<---HEXAGONAL, minimum symmetry one 6-fold axis. Examples are emerald, zincite and apatite



<---CUBIC, minimum symmetry four 3-fold axes. Examples are fluorite, garnet and diamond




Rocks The materials that make up the Earth's crust. They are composed of one or more minerals, but unlike minerals rocks do not usually have a uniform composition. They are usually, but not always, hard. Clay and gravel are classed as rocks, but they are not solid in the way, say, granite is.
For the three main types of rock, igneous rock, sedimentary rocks and metamorphic rocks.
The study of rocks is petrology