How can you tell the difference between plagioclase and potassium feldspar? Please be very specific.
Two answers:
saratogarox
2013-03-15 21:37:01 UTC
The most definitive methods involve either chemical or optical analysis. For field or lab purposes, the two major differences are that plagioclase feldspar usually has the presence of fine, parallel lines or striations on the broken faces or cleavage planes. Also, the color can usually give some direction. Although color is not always reliable, most of the time, plagioclase is some shade of white to a light gray, while orthoclase (K-spar) is generally a light cream to a pink color. The striations are considered the more reliable of the two lab or field observations. The web site referenced below shows a good picture of striations on plagioclase.
Ron
2013-03-16 06:59:02 UTC
Plag can show striations, k-spar has lamellae.
Plag has little tiny parallel grooves on a cleavage surface called striations.
K-spar has a coloration feature called lamellae, which is a pattern of subparallel light-colored stripes that penetrate through the mineral.
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