ARCGems.com Gemology Blog

Friday, July 08, 2005

Quartz Crystal Forms: Trigonal Crystal System

Here is the answer to the earlier quiz. I have labelled different 'forms' of Quartz crystals in the picture, by the following:
a. P: Prism
b. MjR: Major Rhombohedra
c. MnR: Minor Rhombohedra
d. Trapezohedron There were no identifiable Trapezohedron in the picture.
e. TBP: Trigonal Bipyramid


A set of similar faces is called a form.
In the picture below some of the faces show Striations. Striations are parrallel lines on some crystal faces. In Quartz these are Prependicular to the C-axis of the crystal. These lines tell us that the crystal may be a Quartz crystal. Other common crystal which has prependicular striations is a Sapphire but sapphire crystals are very small in size and very different in shape. Beryl (Aquamarine) and Tourmaline don't have Prependicular Striations. I remember long time ago someone was trying to sell me a quartz crystal saying it was Beryl!