Crystal Glossary
The crystal-shop words worth knowing.
A practical glossary for reading listings, labels and mineral descriptions without pretending every retail term is a formal geological grade.
Aura coating
A thin metallic coating applied to a mineral, commonly quartz, to create an iridescent surface. The colour is treatment-created.
Cabochon
A stone cut with a smooth, usually domed surface instead of facets.
Cleavage
The tendency of a mineral to split along particular planes in its crystal structure. Good cleavage can make a hard-looking specimen surprisingly fragile.
Cluster
A group of crystals growing together. In retail, the term is sometimes used loosely, so photographs matter.
Composite
A product made from more than one component, such as mineral fragments combined with resin or other material.
Crystal habit
The characteristic external shape a crystal tends to develop as it grows, such as cubic, prismatic or tabular.
Druzy
A surface covered with many tiny sparkling crystals.
Dyed
Colour introduced artificially, often into porous or fractured material such as some agates.
Fracture
How a mineral breaks when it does not split along cleavage planes. Quartz commonly shows conchoidal fracture.
Geode
A hollow or partly hollow rock cavity lined with mineral crystals.
Hardness
Resistance to scratching, usually described with the Mohs scale. Hardness is not the same as toughness or resistance to breaking.
Heat treatment
Controlled heating used to alter colour or appearance. Heat-treated amethyst sold as citrine is a common retail example.
Imitation
A material made to resemble another material without having the same composition or crystal structure, such as coloured glass sold as a mineral.
Inclusion
Material, fluid, gas or another mineral trapped inside a crystal during or after growth.
Locality
The geographic place a mineral specimen came from. Precise mine-level locality is more informative than a country name alone.
Lustre
How light reflects from a mineral surface, described with terms such as vitreous, metallic, pearly or silky.
Matrix
The host rock or material on which crystals formed or remain attached.
Mohs scale
A relative 1–10 scale of scratch resistance, from talc at 1 to diamond at 10.
Natural
Formed by geological processes rather than manufactured. “Natural” does not necessarily mean untreated.
Phantom
A visible outline of an earlier crystal growth stage inside a later layer of the same crystal.
Provenance
The documented history of a specimen’s source, ownership or acquisition. Provenance quality can range from a vague supplier claim to a retained mine/dealer label and traceable chain.
Stabilised
Material treated with resin or another substance to improve durability or cohesion.
Synthetic
Material grown by people with essentially the same composition and crystal structure as its natural counterpart. Synthetic is not the same as imitation.
Treatment
Any human process used to change a mineral’s appearance, durability or colour, including heating, dyeing, coating, irradiation or resin filling.
Vug
A cavity in rock that can contain crystals, similar to the space inside a geode but not necessarily a separate rounded object.