feldspar betydelse and definition

Exempel på feldspar

• It contains a large proportion of mica, a small proportion of quartz and still less feldspar, but generally an abundance of iron pyrites in very minute crystals, which, on exposure, are decomposed. 

• It is the metallic base of mica, feldspar, slate, and clay. 

• It was made of black, glassy lava mixed with bits of feldspar. 

• The purest clay found in nature is porcelain clay, or kaolin, which results from the decomposition of a rock composed of feldspar and quartz, and it is almost always mixed with quartz. 

• What little feldspar there was is reduced to quartz and mica, and the quartz pebbles are drawn out into lenses. 

• This is conspicuous for biotite and amphibole crystals but less so in the strongly altered feldspar crystals.

• In these first five zones, some crystals, mainly feldspars, are visible in hand specimen.

• The presence of quartz-filled microcracks in feldspar crystals suggests that deformation continued during cooling and crystallization.