Meriden Mineral Club
Crystal Shape
Crystal shape results from an orderly arrangement of the mineral at the atomic level. The actual shape typically conforms to one of 1 of 7 possible "Crystal Systems." The following are examples of mineral crystals with shape:
Shape by Crystal
Quartz is the 2nd most common mineral on the surface of the Earth. It has a complex lattice structure too involved to discuss here. Below is the textbook shape of the ideal quartz crystal and a special form called a phantom crystal.
Garnet
This is a 1 1/4 inch dark red garnet crystal. It is the most common garnet, being an iron aluminum silicate garnet. It has 12 faces so it's called a dodecahedron (12 face object). Each face has 4 sides, which is the shape called a rhombus (geometry 101). You may have seen this comming: it's a Rhombic Dodecahedron! This the most common garnet crystal shape.
Garnet
(Trapezohedron)
Some garnet crystals have 24 faces. Each face is shaped like a trapezoid (again geometry 101). So those garnet crystals are call trapezohedrons. And if that's not enough, there are 36 and 60 sided garnet crystals. The final shape of a garnet crystal is determined by the characteristic during formation at each particular location.
Garnet
(Grossular)
Not all garnets are red! Here is an example of green grossular garnet from Mexico. Grossular garnet is the calcium aluminum garnet.
Smokey Quartz
How about two superbly clear smoky quartz crystals grown together with a third at about right angles? The largest crystal is 4 3/4 inches long. The crystal faces are transparent and the crystal face edges are undamaged. This specimen is truly an object of beauty.
Magnetite
Returning to basic shapes, how about this magnetite crystal of 8 faces, called an Octahedron? Like garnet, this is one of the Isometric shapes. Magnetite is an Iron Oxide mineral. And, yes it will be attracted by a magnet.
Quartz Cluster
These are always favorite specimens for collectors.A cluster of quartz crystals from Arkansas. Instead of just a single crystal, a group of crystals started growing outward simultaneously, all clumpted together from a single source.
Topaz
This is a rare sample of orange topaz. Most topaz is colorless or blue. It is of pure faceting quality. But as a specimen it has a twin structure, two crystals having grown together. The type of topaz example that is not impossible, but hard to find at shows.