Is a mineral a crystal or is a crystal a mineral? Rocks, crystals, and minerals. What’s the difference?
Before explaining the differences between minerals, crystals, and rocks, you need to know the difference between an element and a compound.
What is an element?
A group of atoms of the same kind form an element. The elements are listed on the periodic table, and you’ve heard of some of them: gold, silver, copper, sulfur, oxygen, and carbon. The chemical formula for an element is just the element. The most common elements in the earth’s crust are: O for Oxygen (about 47%), Si for Silicon (about 28%), Al for Aluminum (about 8%), Fe for Iron (about 5%), Ca for Calcium, Na for Sodium, K for potassium, and Mg for magnesium.
What is a compound?
Compounds, on the other hand, are made up of molecules that have different kinds of elements in them. For example, table salt has sodium (Na) and Chlorine (Cl) in it. Sodium chloride is a molecule, and a bunch of sodium chloride molecules together are a compound. The chemical formula for sodium chloride is NaCl. (Note that there are two different elements listed in that formula.)
Now that you know what elements are compounds are, you can understand the definition of a mineral.
What are minerals?
Minerals are made of compounds. Table salt is a mineral with a formula of NaCl. Epsom salts are a mineral with a chemical formula of MgSO4. Minerals have a definite and fixed chemical formula.
Minerals are solids. Liquids are not minerals, so while water is not a mineral, snowflakes are.
Minerals are made by inorganic processes. Minerals are made by natural processes, such as magma cooling under the earth, precipitation, and condensation. Minerals are not made inside living organisms. So, feldspar is a mineral, but a kidney stone, even if it has a consistent chemical formula, is not a mineral.
Minerals are formed of molecules in repeating pattern, called a lattice. The molecules in the minerals join together in repeating patterns. Common patterns are cubic, tetragonal, hexagonal, monoclinic, orthorhombic, trigonal, and triclinic.
Crystals are a special type of mineral.
Crystals are a special kind of minerals. They are a subset of minerals. So, while all crystals (not made by biological processes) are minerals, not all minerals are crystals. Crystals are minerals that have flat faces that meet at regular angles. A lot of geologic time and room to “grow” are required for large, beautiful crystals to form.
Rocks are composites of one or more different minerals. For instance, granite is a rock. It does not have a uniform structure. It’s a mush, usually made of feldspar, quarts, and mica. You can usually look at a piece of granite and see the black mica, pink feldspar, and white quartz.
That ol’ Venn diagram
So, if you picture a Venn diagram (circles inside of circles), the smallest circle is the crystals, since crystals are a special case of minerals. The crystals circle is entirely enclosed in the Mineral circle, and the Minerals circle is entirely enclosed in the Rock circle.