CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Feldspar. View of feldspar crystals. Feldspar is the most common mineral in the Earth's crust. Most feldspar crystals are blocky and they are often twinned. They are found in igneous and metamorphic rocks. The potassium or alkali feldspar series ranges from those containing pure potassium to those with pure sodium along with aluminium, silicon and oxygen. The plagioclase feldspar series ranges from those with pure sodium to those with pure calcium.
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