RocksnGems

ROCK & MINERAL TERMINOLOGY by Al Brown

Everbody loves the beauty of natural rocks and minerals. However, not everyone knows the meaning of all the terms used in the industry. I've prepared this guide to help people understand
more about the item they are thinking about buying. Following are some of the common terms and their definitions:

High Grade High-grade material is exceptionally good. Also, to high-grade a mineral collection is to sort out the best specimens.

Mine Run This is usually used to state that the material is sold as it comes out of the mine. The good and the bad are mixed, and it has not been sorted or high graded.

Pseudomorph When mineral completely replaces another but retains the same outer shape of the mineral.

Drusy is a layer of crystals that formed within a cavity of rock. Amethyst crystals are often found in a drusy. The inner cavity of agate geodes is often line with tiny
sparkling quartz crystals. These crystals reflect (or appear to be) the color of he rock underneath.

Inclusion An inclusion is a particle of foreign matter contained within a mineral or gemstone inclusions can be solid, liquid, or gaseous. A water-filled pocket is called an
enhydro. Organic inclusions are only found in amber. Inclusions are natural and not always considered flaws.

Flaw A flaw is an imperfection found in a mineral or rock. Flaws include cracks. chips, or "dings", and some natural inclusions or fractures. A flawless stone is called "clean".
Flaws can sometimes greatly reduce the value of a stone.

Fracture A crack in a mineral or rock can be natural or man-made. It can be naturally healed, meaning something had happened; perhaps the ground has shifted and
cracked, and then, the crack was filled with natural materials.

Translucent Translucent materials allow some light to pass through them, but the light is difused. the material appears to glow.

Chatoyancy Chatoyancy is a lustrous, cat's-eye effect found in some stones and minerals. In chatoyant material, light is reflected in thin bands within the mineral or stone.
Chatoyancy arises from either the fibrous structure of the material, or from fibrous inclusions or cavities within the stone. The name comes from the French word for "cat's eye"
because it resembles the slit eye of a cat.

Fluorescence Fluorescence is when visibile light is emitted from an object during exposure to invisible radiation. Ultraviolet light can produce vibrant red, yellow, green, blue,
yellow and other colors in a variety of minerals. Some 500 minerals are fluorescent.

Iridescent An iridescent object displays many lustrous, changing colors. Iridescence is caused by dispersion of light in cracks and flaws resulting in a rainbow-like display of
colors (often seen in soap bubbles or oil slicks). Colors tend to change as the angle of viewing changes. The word comes from the Greek word "iris", which means rainbow.

Cabochon (AKA "Cab" for short) is a stone cut for jewelry. It is usually rounded, or domed, and polished on top, and flat or slightly rounded on the bottom. Stones can be
calibrated (cut to a certain size/shape). This form of cutting is normally used for opague or translucent stones, but is sometimes used with transparent stones with too many
inclusions to make a good faceted stone. Faceted is the way diamonds are cut with tables and angles.

Metaphysical Some people believe certain rocks and minerals have "healing" abilities. The metaphysical system of treating diseases is based upon diving science of mind and
affirmative prayer bringing health and harmony in every situation. The term, "healing", is a holistic concept that extends beyond the body to encompass the mind, emotions, and
spirit. Some believe we can "heal" relationships, emotions, self-esteem, and sick financial situations.

Opague Opague means no light passes through the material.

Vug This is a natural hole or hollow in a rock. Also called a pocket or cavity

Botryoidal This literally means "cluster of grapes" and is used to describe a rock that has a bumpy or grape-like surface.