# The Six Crystal Families

## by geofablab, published Oct 21, 2013

The Six Crystal Families Oct 21, 2013
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# Summary

All minerals fall into one of six crystal classes based on the ordering of their component elements and polyatomic ions.

Isometric, a=b=c, alpha=beta=gamma=90 degrees

Tetragonal: a=b<>c, alpha, beta, and gamma equal 90 degrees

Orthorhombic: a, b, and c are unequal; alpha, beta, and gamma equal 90 degrees; a=20, b=30, c=40

Hexagonal: a=b<>c; alpha=beta=90 degrees, gamma=120 degrees;

Monoclinic, a, b, and c are unequal; alpha and gamma = 90 degrees, beta does not equalÃÂ 90 degrees

Triclinic: a,b, and c are unequal; neither alpha, norÃÂ beta, norÃÂ gamma equalÃÂ 90 degrees

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Hi geofablab,

I noticed that your monoclinic body has a beta angle of exactly 120 degrees, which makes it trigonal or hexagonal (in fact the two objects cc_trigonal.stl and cc_monoclinic.stl are identical). Of course beta=120 is allowed in the monoclinic system, but would it not be better to avoid a special case for educational purposes?

Cheers,

Peter

geofablab - in reply to pmueller

Peter...thanks for the suggestions. I have updated the models to remove the trigonal system as it is a subset of hexagonal family.

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