“Tartan plaid” or “plaid” twinning is a combination of albite and pericline twinning. It is the dead giveaway of microcline.
In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). You can find the explanation on the alkali feldspar page.
3D framework of linked tetrahedra
|Habit||Prismatic, stubby to elongate
|Cleavage||Perfect (001), good (010)|
|Fracture||Conchoidal to uneven|
|XPL||1st order greys
|after Perkins, 307-308|
Microcline in Hand Sample
Amazonite (green microcline)
Microcline in Thin Section
We wouldn’t normally circle the mineral in question on the slide. For some reason, almost everyone has trouble identifying microcline at first, so we thought we’d throw you a bone.