Fieldwork - Know your Crystal & Mineral Shapes
Minerals come in a variety of colours and have a variety of properties. However form habits can often be the most identifying factor. Here are some basic forms to help you get started in identification.
Equant- Having the same diameter in every direction.
Prismatic- Elongated in one direction.
Acicular or radiating- Needlelike or often crystals growing out from a central point
Example: natrolite and wavellite.
Tabular- Appears as thick or thin flat plates.
Striated- Having very shallow parallel grooves or depressions on one or more crystal faces.
Bladed- Broad and flat, elongated like a knife blade.
Globular- Resembling a bunch of grapes or linked bubbles.
Massive- Interlocking mineral grains that lack apparent structure.
Dendritic- Crystallizing in a "tree-like" or branching pattern.
Gemstone- A mineral or crystal that can be fashioned into a jewel. This is determined by color, transparency, brilliance and hardness for cutting and polishing. Example: Diamond, Rubies, Emeralds, Amethyst
Know your Rock Types
Crystals and Minerals can be found with different types of rocks. Here examples to help you know what to look for: (For occurrences in BC of each rock type click on the Map button).
Igneous rocks are formed through the process of molten material such as magma, extruding upwards from deep within the earth. If the magma reaches the surface, it then quickly cools and forms crystals. The term for this is extrusive (volcanic). If the magma does not reach the surface, it cools slowly to form massive crystals. This is known as intrusive (plutonic).
Basalt is an example of extrusive igneous rock. It contains cavities or amygdules which have resulted from gas bubbles that were trapped as the rock suddenly hardened. From the outside this geode or thunder egg might appear like any other rock. But if you were to crack it open, what would you find? You might find agate, amethyst, chalcedony, calcite, or zeolites. Every geode is a possible treasure waiting to be discovered.
Pegmatite is an example of intrusive igneous rock. It commonly occurs around dikes associated with granitic rocks and generally can be found with large crystals of quartz, feldspar and biotite. Unlike extrusive rock who’s texture is glassy, intrusive's texture is coarse. Pegmatite has been known to contain large crystals such as beryl, garnet, spodumene, fluorite and muscovite.
Sedimentary rocks, also known as conglomerate, are formed by the compaction of sediments such as sand, gravel, or clay, or by chemical precipitation to form rocks such as chert or travertine. Other examples are Jasper, Rhodonite, Gypsum and Limestone.
Metamorphic rocks are formed by the alteration of older rocks (igneous and sedimentary) reforming with considerable heat and/or pressure deep within the earth. The types of minerals present are affected by what the original rock type was.
As mentioned, through heat and pressure the sedimentary may be altered to become a metamorphic rock like serpentinite which may come originally from jade, soapstone, rhodonite, idocrase, and chalcedony.
Marble is the result of metamorphosed limestone. In this rock you might find: garnet, scapolite, tourmaline, epidote and wollastonite. Schist and gneiss rock may contain garnet, staurolite, sillimanite, andalusite, kyanite, rutile, corundum and spinel.
For more information on these stones and other minerals not listed you can contact the Gem Hunters or visit the local BC Geological Survey Branch.