Metamorphism
Changes in rocks brought about by heat and pressure from in the rocks just below the surface.

Meteorite
Solid object that comes from outer space and falls to earth; made up of metal material, usually magnetic.

Mineralogist
A person who studies the formation, occurrence, properties, composition and classification of mineral specimens.

Mineraloid
A mineral-like substance that does not have a crystal structure and possesses a chemical composition that varies beyond the accepted range for a specific mineral.

Mineralogy
An earth science focused on the chemistry, crystal structure and physical properties of minerals, their distribution and identification.

Mineral
A natural, inorganic, solid compound having a specific chemical composition, formed through geological processes.

Miner
A person who excavates and searches for gemstone and mineral specimens.

Minero
The Spanish word for "miner".    (see above)

Mines
Underground areas and caves where precious, semi-precious gemstones and minerals are excavated. The plural version is 'mine'.

Minas
The Spanish word for "mines". The plural translation is 'mina'.    (see above)

Moh's Hardness Scale
The numerical scale developed by Friedrich Mohs in 1822 that assigns a rating to a gem according to its ability to resist scratching, with the hardest being 10 and the softest being 1.

The hardness of a mineral is an easy diagnostic test to perform to attempt to identify an unknown mineral. For example, if mineral X scratches mineral Y, and mineral Y does not scratch mineral X, then mineral X is harder than mineral Y. If mineral X and Y both scratch each other, then their hardness is equal or very similar.

Hardness is rounded off to the nearest half number. The 10 minerals in the scale are:

Mohs scale is very useful but it is not linear. The minerals chosen were selected only because of their popularity. Number 10 on the scale (diamond) is 140 times harder than number 9 (corundum), whereas 4 (fluorite) is only 1.11 times harder than 3 (calcite). A proportional measurement, called absolute hardness, was recently devised, but is currently only used by scientists who need the most accurate of results. The Mohs scale is the standard used by mineral collectors only.

Absolute Hardness
The Mohs Hardness Scale is relative. Fluorite at 4 is not twice as hard as gypsum at 2; nor is the difference between calcite and fluorite similar to the difference between corundum and diamond. An absolute hardness scale looks a little different than the relative scale. Most minerals are close in hardness. But as hardness increases, the difference in hardness greatly increases as seen in the absolute hardness scale pictured here.

Using an absolute scale you can say that corundum is actually 4 times softer than diamond, not half as soft like the Mohs relative hardness scale shows.

Natural Gemstone
A mineral, stone or organic material that can be cut and polished or otherwise treated for use as jewelry. A “precious” gemstone has beauty, durability and rarity, whereas a “semi-precious” gemstone has only one or two of these qualities.

Opalescence
A variety of iridescence that is most often a light blue glow in color.

Opaque
Not transparent or translucent.

Organic Gem
Matter that is not technically a gemstone, but is derived from animal or plant life. Organic gems include amber, coral, ivory, pearl and tortoise shell among others.

Pearl Essence
A liquid coating that adds a pearl like luster to simulated pearls. It is derived from the scales of a herring fish.

Points
Units of measurement to express the carat weight of a gem. One carat is equal to one hundred points.

Potch
Native material around a gemstone, like ironstone surrounding opal.

Precious Gem
The quality of a gem that has beauty, durability and rarity.

Precious Metals
Defined by the industry as gold, silver and platinum, the term 'precious' is still widely accepted to delineate metals.

Primary Deposit
When a gem or mineral is found resident in its original host or mother rock.

Polisher
A person who cuts and polishes a variety of gemstones and minerals.

Pulidor
The Spanish word for "polisher".    (see above)

QUARTZ
Formed from the two most abundant elements in the earth's crust: silicon and oxygen. Quartz has a high thermo-conductivity, which makes it feel cool to the touch. Historical records show the use of quartz crystal for decoration and jewelry for at least the past 4,000 years. Spiritually, they are also able to structure, store, amplify, focus, transmit and transform energy, which includes matter, thoughts, emotions and information. (click the subject title for more indepth information)

Reconstructed Stones
The old method of fusing stones made from chips and other unusable pieces of stone.

Refraction
The bending of light passing through one medium to another, most often occurring with quartz.

Refractive Index
A process developed by Willebrord Snell that incorporates a refractometer to measure the speed and angle of light as it enters a gemstone. It is used for critical gem identification.

Rough
In gemology, this refers to the raw, natural state in which gems are found.

Rutiles
A titanium dioxide mineral with needle-like inclusions (or foreign matter) within a stone. The rutile needles can be reddish (which is what rutile means in Latin). Often found embedded in quartz; can also produce some amazing gem phenomena as a star and a cat's eye in sapphire and other gems.

Rutilated
The same as above (rutiles), describes the type of specimen inclusions.

Secondary Deposit
A deposit of gems that has been worn away from its original site, usually by the effects of weather. An alluvial deposit is an example of a secondary deposit.

Sedimentary Rocks
Originally formed of sediment, including shale and sandstone, composed of fragments of other rocks deposited after transportation from their original source. Including those formed by precipitation, or by the secretions of animals as in certain limestones.

Semi-precious Gem
Containing one or two of the qualities of a 'precious' gem - beauty, durability or rarity.

Sheen
Another name for iridescence, usually found as silvery or golden in some obsidian specimens.

Synthetic Gemstone
A man-made stone that, unlike a simulant, has the same chemical composition and crystal structure as its natural counterpart.

Transparency
The degree to which light passes through a material.

Trichroism
Gems that display three different colors when viewed from different angles.

Triplet
A man-made stone of three parts that includes a clear protective top layer fused together with a thinly sliced gem, a dark backing material and a clear or colored adhesive.

Tumbling
The simplest form of gem polishing, in which the rough mineral is put into a revolving barrel with progressively finer abrasives, until a fine polish is obtained.

TURQUOISE
Found in many countries around the world, with specimens from the United States, México, Iran and Afganistan being the most sought after in valuable. An isomorphous mineral with chalcosiderite. Generally cut as a cabochon gemstone but frequently faceted or engraved. Often has an attractive blue or sky-blue color of fine-quality. (click the subject title for more indepth information)

Veins
In gemology this term is loosely used to describe long thin lines that occur on the surface of the gem. The black lines seen in turquoise or howlite are two example of these veins.

Vug
An open cavity in rocks, often lined with crystals.

Xenolith
Rock enclosed in volcanic magma.