The alkali feldspars are those within the alkali feldspar solid solution series.

Amazonite
Microcline
Orthoclase
Sanidine

In thin section, alkali feldspar grains often appear to be sprinkled with dirt (PPL) or tiny confetti (XPL). Feldspars weather readily to a fine-grained white mica called  sericite.  Unless it’s heavily altered, you’ll still be able to identify the underlying alkali feldspar by rotating the stage and looking for its wispy lamellae.