Feldspars are a group of aluminum silicate minerals that typically form in igneous environments or are found in metamorphic rocks, comprising the most abundant mineral group on Earth. Depending on the chemical composition, feldspars further subdivide into potassium feldspars and plagioclase feldspars. Potassium feldspars bear potassium, K, ions while plagioclase feldspars bear either sodium, Na, or calcium, Ca, ions. Potassium feldspars are comprised of three mineral polymorphs: orthoclase, sanidine, and microcline meaning that all three share the same chemical composition but differ in crystalline structure. Without optical analyses, it is much more difficult to distinguish which polymorph you have in a hand sample since they share similar physical properties and can simply be referred to as potassium feldspars. Though it is typically difficult to distinguish K-feldspars by appearance, it should be noted that an occasional deep green colour, as exhibited by sample A and is characteristic of microcline. Samples B and C exhibit more common colours of white and shades of pink and red. Feldspars have a blocky habit, hardness greater than glass (6-6.5), two cleavage planes meeting at nearly 90°, as well as a vitreous-earthy-porcelaneous and opaque character. To further physically distinguish potassium and plagioclase feldspars apart, plagioclase typically appears chalky, dull, and white to grey and may exhibit lamellar twinning striations on some cleavage surfaces (see Plagioclase sample). K-feldspars completely lack these striations and typically exhibit perthitic texture, as exemplified in samples A and B by the x indicator. Microscopically, plagioclase will diagnostically have polysynthetic twinning, prominently albite twinning and sometimes occurring with Carlsbad twinning, while K-feldspars only contains simple Carlsbad twinning.