Resize Text: Quartz is the most abundant oxide in the earth's crust and occurs as both large- and fine-grained crystals. The optical microscope is necessary to distinguish between the fine-grained varieties; thin sections allow the microcrystalline types to be divided into two groups. Chert, flint, and jasper tend to show a granular structure, whereas chalcedony reveals a fibrous growth. Agate is banded chalcedony.
| January-February 2010Agates from Western Australia Found in a 3,480-Million-Year-Old Host Rock
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