Potassium Feldspar Thin Section
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Potassium feldspar thin section. As the magma evolves toward more fe rich compositions the chromite also becomes more fe rich and less transparent. Plagioclase feldspar thin section view description. Orthoclase and sanidine are stable above 500 c and 900 c respectively.
Sanidine is usually distinguished rather easily from the other alkali feldspars because it typically appears glassy i e it tends to be colourless and much of it is transparent. Potassium feldspar comes in three different crystal structures that depend on the temperature it formed at. Microcline is the stable form below about 400 c.
The ideal value for the potassium rich alkali feldspars is 2 56 which is less than the lowest value for the plagioclases namely 2 62 for albite. Cr mg al rich chromites are realtively transparent and can be dark brown at full thin section thickness. K feldspar in thin section rarely has well developed cleavage but two cleavage planes may be visible in some crystals.
To link to this object paste this link in email im or document to embed this object paste this html in website. You can find the explanation on the alkali feldspar page. Orthoclase orthoclase is frequently known as potassium feldspar or k spar and is easily distinguished from the plagioclase feldspars in hand sample by its lack of striations.
Fe rich chromite is typically opaque at full thin section thickness but is transparent dark brown along thin edges. Home rocks and minerals plagioclase feldspar thin section reference url share.
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