Optical Mineralogy - Crystal Systems

Isometric

Means equal measure, refers to the equal crystal axes

How many crystal axes do isometric crystals have, and what angles do they meet at?

Three axes that meet at 90 degrees in the center

Hexagonal crystal subgroups

Hexagonal and trigonal

Axes of Hexagonal crystals

Three horizontal axes at angles of 120 degrees, and one perpendicular c-axes through the middle

Tetragonal crystal axes

Two equal horizontal axes that are perpendicular to each other, one c-axis.

Which two crystal systems are uniaxial

Hexagonal and tetragonal

Orthorhombic crystal axes

3 mutually perpendicular axies of diffrent lengths

Monoclynic crystal axes

Axes of unequal length, where a & b are perpendicular, b & c are perpendicular, but a & c are not

Triclinic crystal system

Three axes, none are equal or perpendicular

Triclinic system symmetry

They have one plane, or none

Examples of isometric crystals

Fluorite, halite, garnet, magnetite, pyrite, sylvite

Tetragonal crystal example

beryl, rutile, zircon