What is the difference between rocks, minerals and gems? A mineral is made of inorganic material - substances that were never alive - and whose atoms are arranged in a regular pattern (or crystal). Rocks are composed of one or more minerals - and include Lapis, clay, sand and limestone. Gems are a special subgroup of minerals, usually rarer, clearer and more visually appealing than other minerals. There is no set rule as to which minerals are definitively gems; it is more a matter of custom.
Precious vs. Semi-Precious
The majority of gems can be divided into precious and semi-precious categories. The term "precious" is reserved for the most rare and expensive of gems - including diamonds, emeralds, rubies, pearls and sapphires. Most remaining gems - including varieties of quartz like Amethyst, Citrine and Bloodstone - are semi-precious.