|Rock and Mineral Terminology |
Everybody loves the beauty of natural rocks and minerals. However, not everybody knows the meaning of all the terms used in the industry. I’ve prepared this guide to help those people understand more about the item they are thinking of buying. Here are just a few of the common terms and their definitions:
High-grade material is exceptionally good. Also to high grade a mineral collection is to sort out the best specimens.
This is usually used to state that the material is sold as it comes out of the mine. The good and bad mixed, it has not been sorted or high graded.
When one mineral completely replaces another, but retains the same outer shape of the replaced 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 lined with drusy of tiny sparkling quartz crystals. These crystals reflect (or appear to be) the color of the rock underneath.
This is a natural hole or hollow area in rock. Also called a pocket or cavity.
This literally means “cluster of grapes” and is used to describe a rock that has a bumpy or grape like surface.
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.
A flaw is an imperfection 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.
A crack in a mineral or rock that can be natural or man made. It can be naturally healed, meaning something happened, perhaps the ground shifted and cracked, and then the crack was filled with natural material.
Translucent materials allow some light to pass through them, but the light is diffused. The material appears to glow.
Opaque means no light passes through the material.
Chatoyancy is a lustrous, cat's eye effect seen in some stones and minerals. In chatoyant material, light is reflected in thin bands within the mineral or stone. Chatoyancy arises either from the fibrous structure of a 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.
Also known as labradorescence, an iridescent object displays many lustrous, changing colors. Iridescence is caused by dispersion of light in cracks and flaws resulting in a rainbow-like play of color (as often seen in an oil slick or a soap bubble). The colors tend to change as the angle of view changes. The word comes from the Greek word “iris”, which means rainbow.
Fluorescence is when visible light is emitted from an object during exposure to invisible radiation. Ultraviolet light can produce vibrant red, green, blue, yellow, and other colors in a variety of minerals. Some 500 minerals are fluorescent.
Cabochon (also known as Cab for short)
A stone cut for jewelry. It is usually rounded (or domed) and polished on top, and either flat or slightly rounded on the bottom. Stones can be calibrated (cut to a certain size/shape) or freeform (an abstract shape). This form of cutting is usually used for opaque or translucent stones, but is sometimes used for transparent stones with too many inclusions to make a good faceted stone (faceted is the way diamonds are cut with tables and angles).
Some people believe that certain rocks and crystals have “healing” abilities. The metaphysical system of treating disease is based on divine Science or 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 our minds, our emotions and our spirits. Some believe we can “heal” our relationships, we can “heal” our emotions, we can “heal” our self-esteem, and we can “heal” a sick financial situation.