Crystal Forms

Crystal Forms Minerals grow into specific shapes They usually crystallize into one of 6 forms Cubic Tetragonal Hexagonal Orthorhombic Monoclinic Triclinic

Axes of Symmetry Lines about which a mineral can be rotated through some angle which brings the object to a new orientation which appears identical to its starting position.

Cubic Crystals shaped like blocks 3 axes of symmetry –All the same length –All perpendicular to each other

Cubic Example: Pyrite

Tetragonal Crystals shaped like four-sided prisms and pyramids. Three axes of symmetry –Two axes are the same length and lie on a horizontal plane. –The third axis is not the same length and is at a right angle to the other two. –All perpendicular to each another.

Tetragonal Example: Zircon

Hexagonal Crystals are shaped like six-sided prisms or pyramids. Four axes of symmetry –Three lie in the same plane, are the same length, and intersect at 120° angles. –The fourth axis is not the same length, and is perpendicular to other three.

Hexagonal Example: Beryl

Orthorhombic Crystals are short and stubby. 3 axes of symmetry –All unequal lengths –All perpendicular to each other.

Orthorhombic Example: Topaz

Monoclinic Crystals are short and stubby with tilted faces at each end. 3 axes of symmetry –All unequal lengths –Two axes lie in the same plane at right angles to each other. –The third axis is inclined.

Monoclinic Example: Gypsum

Triclinic Crystals are usually flat with sharp edges, with no right angles. 3 axes of symmetry –All unequal lengths – None are perpendicular to one another.

Triclinic Example: Feldspar

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ASSIGNMENT PG 63 SHOWS THE SIX MAIN CRYSTAL SYSTEMS YOU NEED TO MAKE 3- DEMENSIONAL MODELS OF THE 6 MAIN CRYSTAL SYSTEMS MAKE SURE TO LABEL EACH MODEL WITH THE SYSTEM NAME AND YOUR NAME