The mineral fluorite is commonly sold in mineral shops as octahedral (8-sided) objects. this shape originates from
a) a pseudomorph (false form) of fluorite from replacement of a salt, potassium chlorite, that grows in octahedral crystals.
b) the growth of fluorite in caves and is the form the crystals grow in the open cavern.
c) the typical crystal form of fluorite.
d) cutting a larger crystal along four perfect cleavage planes, forming a cleavage fragment.