Crystals, Gemstones & Fossils
Crystals -- In science, a crystal is a solid substance in which the atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The word crystal is a loan from the ancient Greek word (krustallos), which had the same meaning, but according to the ancient understanding of crystal. At root it means anything congealed by freezing, such as ice. The word once referred particularly to quartz, or "rock crystal". Most metals encountered in everyday life are polycrystals. Crystals are often symmetrically intergrown to form crystal twins.
Gemstones -- A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive mineral, which - when cut and polished - is used to make jewelry or other adornments. However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry and gemstone rings, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.