2-3 Crystal Chemistry

CRYSTAL CHEMISTRY Chapter 2, Section 3

The Physical Properties of Minerals

qMinerals- a naturally occurring solid that has a crystal structure and a definite chemical composition qScientists identify minerals by looking at the physical properties of color, shininess, density, crystal shape, hardness, and magnetism.

Bonding in Mineral Crystals Ionic Crystal Arrangement of particles in a mineral and the kind of bonds holding them together determine physical properties such as crystal shape, hardness, and the way the crystal breaks apart When bonds in an ionic crystal break, they break along a face of ions A blow shifts the ions so + ions are next to other + ions and near – ions Creates a weakness in the crystal Smaller crystals retain the cube shape

Molecular crystal Covalent bonds are much stronger than ionic bonds Doesn’t have clear lines of weakness Cannot be crushed into predictable shapes Example- Quartz (SiO2)

Comparing Crystals qProperties such as hardness depend on the strength of the bonds in a crystal qStronger bonds yield harder crystals qSome covalent bonds are stronger than quartz