I have a piece of rock that I believe to be potassium feldspar but I'm not certain.
The rock leaves a white streak, can scratch glass and be scratched by a penknife and has a pearly luster on unbroken faces.
There are inclusions of quartz and what I assume to be mica through the rock. There is a browner material also spread through the specimen and on one side there is a black material, pyroxene maybe?
The piece was found in Co Tyrone, Northern Ireland.