The only sure way to identify a plagioclase feldspar from a potassium feldspar on large enough specimen to see with the naked eye is to ________.
A)compare their colours, plagioclase is always darker
B)find multiple parallel twinning striations on a cleavage face
C)measure their exact cleavage angles, plagioclases have 120°
D)find wormy exsolution lamellae going obliquely across the cleavages

Question

The only sure way to identify a plagioclase feldspar from a potassium feldspar on large enough specimen to see with the naked eye is to ________.
A)compare their colours, plagioclase is always darker
B)find multiple parallel twinning striations on a cleavage face
C)measure their exact cleavage angles, plagioclases have 120°
D)find wormy exsolution lamellae going obliquely across the cleavages

Quizplus · Accepted Answer

Parallel twinning striations are a distinctive feature of plagioclase feldspar and can be used to differentiate it from potassium feldspar. The other options may not always apply or may not be reliable methods of identification.

The Only Sure Way to Identify a Plagioclase Feldspar from a Potassium