Physical Properties of Minerals main content.

Physical Properties of Minerals

Part of Harry Frank Guggenheim Hall of Minerals.


Exhibition Text

Audio Transcript
The physical properties of a mineral depend on the kind of atoms it is composed of and, more critically, the way these atoms fit together to form the mineral's crystal structure.
Near the top of this case on the left, you will notice two models showing the atoms in the crystal structures of two minerals with actual specimens displayed above them. In both instances, the atoms involved are those of the element carbon. In the structure of the mineral diamond, on the left, the carbon atoms are spaced the same distance apart and are covalently bonded tightly together. This arrangement causes the great hardness of diamond and its inert chemical characteristics.

In the other mineral, graphite, also made of carbon, the carbon atoms are quite strongly bonded, and closely packed, but only in a plane, as you can see in the model. As right angles to this plane, the atoms are weakly bound. Weakness along a plane allows graphite to be soft and easily split, or cleaved. This is why graphite pencil leads leave a mark on paper.

The atomic structure of all minerals determines their physical properties, as illustrated by the large block of mica, and its well-developed cleavage. The minerals on the right in this case show important physical properties, which are useful not only in identifying minerals but may make them useful to us.

In this series of 10 minerals at the top, each successive mineral is harder than the ones to its left. This series, first organized by the geologist Frederick Mohs, is known as t