- Amorphous:
- Not having crystalline properties, as glass, amber, and opal.
- Anatectic:
- Having melted from preexistent rock.
- Asterism:
- A star effect by some gems when viewed under strong light.
- Carat:
- A unit of weight (one-fifth of a gram by which gemstones are weighed.
- Chatoyant:
- An optical phenomenon resembling the narrow pupil of a cat’s eye seen when a stone is tilted under a strong light.
- Clasts:
- Fragments of rocks or minerals resulting from the mechanical breakdown of another rock.
- Contact rocks:
- Rocks in contact with, or near, an igneous intrusion that have been metamorphosed by the heat of the intrusion.
- Cubic:
- The shape of a gaming die.
- Dichroic:
- Showing two colours when viewed through a dicroscope.
- Dike:
- A vertical to sub-vertical intrusive sheet.
- Evaporite:
- Sedimentary rock or mineral that precipitates from solutions through evaporation.
- Extrusive:
- Pertaining to igneous rocks that solidify on the surface of the earth.
- Facet:
- A polished, flat plane on the surface of a cut gem.
- Fluorescent:
- Appearing to have one colour when viewed in normal light and to glow a different colour when viewed under ultraviolet light.
- Gemstone:
- Any naturally occurring material that happens to be regarded as valuable.
- Hexagonal:
- The shape of having a symmetry of a six-fold vertical axis.
- Hypabyssal:
- Pertaining to a shallow intrusion.
- Igneous Rock:
- A rock formed from molten material, magma if underground, or lava if erupted onto the surface.
- Intrusive:
- Pertaining to igneous rocks that solidify beneath the surface of the earth.
- Metamorphic Rock:
- A rock altered by heat and/or pressure.
- Metasomatic:
- Having changed because of addition or loss of chemical components.
- Mineral:
- A material in which all specimens have the same chemical formaula and crystal symmetry.
- Mohs’ Scale of Hardness:
- Based on the ease of scratching one of its surfaces with the sharp edge of a mineral of known hardness.
- talc
- gypsum
- calcite
- fluorite
- apatite
- orthoclase
- quartz
- topaz
- corundum
- diamond
- Monoclinic:
- The shape in which no pair of crystals has the same length, width, or height as any other, and having a two-fold axis.
- Opalescent:
- Showing a display of colours across the surfaces.
- Opaque:
- Through which light cannot travel.
- Orthorhombic:
- The shape having three faces that are unequal in length, width, and height, but at right angles to each other.
- Pleochroism:
- An optical phenomenon whereby a stone appears to change colours when viewed from different angles and in different lights.
- Porphyritic:
- Consisting of feldspar crystals embedded in a compact fine-grained base material.
- Regional Metamorphism:
- Metamorphism that affects vast areas of the earth’s crust.
- Rock:
- A combination of several different minerals, although occasionally only one.
- Sedimentary Rock:
- A rock formed by the accumulation and consolidation of layers of loose sediment, or by the accumulation of chemicals that precipitate out of water.
- Tetragonal:
- The shape of a box that has had its top and bottom removed, an open shape which needs to combine with other shapes to make a complete crystal.
- Translucent:
- Transmitting light imperfectly so that one cannot see through a material clearly.
- Triclinic:
- The shape of having no face with the same dimensions and not at right angles to any others.
- Trigonal:
- The shape with three equal axes, equally inclined, but not at right angles to each other.
- Variety:
- Different types and colours of a gem within a species.
