My favorite mineral Olivine. A magnesium iron silicate (Mg,Fe)2SiO4 found in igneous rocks, as a hand specimen it glimmers its nearly emerald green color. Yet as a thin section in PPL (Polarized Light) it conceals itself in a nearly colorless hue. But don’t astray and forget to view in XPL (Cross Polarized Light) as radiates in bright 3rd order color through a straight extinction. The bright pink and purple speaks to me!
Thin Section of Olivine seen in XPL (Source: Carleton College)
Olivine crystals in Granite (Source: LondonGranite.com)