English: This image shows a crankshaft chain of aluminosilicate tetradehra that is a basic element of the feldspar crystal structure. The particular feldspar depicted is anorthite. White spheres are oxygen ions; red are calcium; blue is aluminium; and black is silicon. Other feldspar minerals share the structure, with different ions (typically sodium or potassium) substituting for calcium and with different proportions of aluminium to silicon. Each cranshaft links with neighboring crankshafts to form a three-dimensional network of fused four-member rings.