The atomic structures of gemstones are similar to their mineral origin, in that their atomic components are arranged in specific patterns, or crystal structures . There are 6 main families or systems of crystallographic configurations (please refer to the section on mineral crystals):
- Isometric System – has three equivalent crystallographic axes perpendicular to each other. Examples are diamond, garnet, spinel and lapis lazuli.
- Tetragonal System – has three perpendicular crystallographic axes; two horizontal axes are of equal length, while the vertical axis is of different length and may be either shorter or longer than the other two. Examples are zircon and rutile.
- Hexagonal System – has four crystallographic axes; three horizontal axes are equivalent in lengths and intersect each other obliquely at 60°; the fourth axis is perpendicular to the horizontal axes and maybe shorter or longer in length. Examples are Corundum, beryl, quartz and tourmaline.
- Orthorhombic System – has three crystallographic axes that are or different lengths but perpendicular to each other. Examples are peridot, chrysoberyl, topaz, sillimanite, tanzanite, and cordierite.
- Monoclinic System - has three unequal crystallographic axes; two of these axes (a and c) are inclined toward each other at an oblique angle and do not intersect one another at right angles; the third axis (b) is perpendicular to the other two. Examples are: orthoclase feldspar, spodumene, diopside, jadeite, and nephrite.
Triclinic System – minerals of this system have three unequal axes, all of which intersect at oblique angles. None of the axes are perpendicular to any other axis. Examples are turquoise, kyanite, and albite.