Crystal Shapes

We're going to move on now to the crystalline structures of gemstones. This will help you gain an even better perspective of gemstone characteristics. Most mineral gemstones are crystalline, with their atoms arranged in regular and symmetrical patterns, kind of like a lattice. There are some that are amorphous, with no or only a weak crystal structure.There can be single crystals or many in a group in crystalline minerals. Polycrystalline minerals are usually made up of many small crystals. In cryptocrystalline minerals, they are too small to see without using a microscope. 

Crystalline minerals are made up of a number of flat surfaces, or faces. The way these faces are oriented defines the overall shape, which is known as the habit. Some minerals have a single, characteristic habit (such as pyramidal or prismatic). There are others that can have several. A lump of crystalline mineral without a definitive habit is called massive. Amorphous gemstones (like tektites and obsidian) have an irregular shape. Let's take a look at examples of common habits:

Amorphous Amber sample

Pyramidal Topaz sample

Acicular Millerite sample

Prismatic Linarite sample

Gemstone massive sample

Dendritic sample

And a quick word about twinning. As we all know, natural crystals are very rarely perfect. Their growth is influenced by all kinds of external factors, such as temperature, pressure, space, and the medium in which they grow. Twinning is an irregularity that can occur when the internal structure of the crystal is repeated. But of course, twins can grow together in any number of different ways. Take a look below:

Topaz twinned with Albite

 

 Okay, well that's enough for this go-round! Next time we're going to cover crystal systems. That's where the Geometry should come in handy. Be prepared to think three dimensionally, haha! You'll need to be able to envision multiple, symmetrical sides. Just letting you know ahead of time! Anyways, thanks for reading, and until next time.