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USGS CMG InfoBank: Mineral's Environment of Formation

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Comment: 17:33 - 19:00 (01:27)
Source: Annenberg/CPB Resources - Earth Revealed - 12. Minerals: The Materials of Earth
Keywords: "J. Lawford Anderson", mineral, "atomic structure", "physical property", diamond, graphite, "environment of formation", "crystal structure", gem, carbon, atom, "covalent bond", "soft bond", hardness

Our transcription: The conditions under which a mineral is created may be clearly reflected in its atomic structure, and, therefore, in its physical properties.
Diamonds and graphite are perfect illustrations of the relationship between the mineral's environment of formation, crystal structure, and physical characteristics.
Diamonds have long been coveted as perhaps the most beautiful and precious of all gems.
Graphite, which is used in pencils is extremely commonplace and far less valuable; yet both minerals are made of the same substance: pure carbon.
The great contrast between their physical properties can be attributed to the differing structural arrangements of their carbon atoms.
Diamond is the hardest of all minerals.
Why is it so hard?
It's because it has a very special and unique covalent bond that holds the different carbon atoms so tightly that they cannot be scratched.
In contrast, graphite, also a carbon mineral, the same carbon atoms are held with a very different kind of bond, and it's a very soft bond, and that mineral becomes soft, and that's why we can use graphite in pencils.
So hardness is one aspect, and it's directly related to the bonding that holds the structure together.

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