It's a rocky start

What is a Mineral?

Minerals are naturally occurring, inorganic solids with a definite chemical composition and a regular atomic structure. From this basis come all their physical properties.

Some of the most obvious physical properties of a mineral are hardness (resistance to scratching), tenacity (resistance to impact), specific gravity (relative density), cleavage (the tendency of some crystals to split along planes of weakest atomic bonding), magnetism, conductivity of electricity, reactibility to acids etc. These measurable physical properties, along with a number of optical ones such as luster, refractive index and selective absorption of light rays, enable minerals to be positively identified by scientific instruments.

Minerals form crystals in one of seven crystal systems. Crystals can be very large, like some quartz crystals from Brazilian pegmatites. Others are too small to see without powerful magnification. Chalcedony, with its structure of interlocking fibrous quartz crystals in hydrous silica is termed microcrystalline.

What is a gem?

A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks and occasionally organic materials that are not minerals are also used for jewelry and are therefore often considered to be gemstones as well.