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.

d) cutting a larger crystal along four perfect cleavage planes, forming a cleavage fragment.

Explanation:

Fluorite Octahedron crystals are formed narutally, but it's not common, they can be found more commonly as cubes, the majority of fluorite octahedron are formed when miners cit them along its natural cleave lines.

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hello!

let's go through all of these words' definitions.

u-shaped valley - where the valley curves down like a u shape

corrie - similar to the hole created at the top of a volcano when it erupts, it's almost like a dent in a mountain

pyramidal peak - a mountain where the peak is very sharp, such as the matterhorn.

arete - two valleys separated by a thin mountain range

i'm going to assume you know how to read a topographic map, but in case you don't, feel free to comment.

now, let's figure out which one's which:

a - seems to be a mountain range separating two valleys, with a mountain running from top center to bottom center and two valleys on either side. therefore, i'd consider this an arete.

b - it looks like a dent into the mountain, like what a corrie is.

c - looks to be a valley, with two steeper sides curving up around the bottom of the valley which has a river in it. i would consider this an u-shaped valley.

hope this !