【Crack】 , 【cleft】 , 【fissure】 , 【crevasse】 , 【crevice】 , 【cranny】 ,  【chink】 are comparable when meaning an opening, break, or discontinuity made by or as if by splitting or rupture.

【Crack】 basically applies to substances or structures that are subjected to drying, slow disintegration, or shrinking or are fragile or brittle.

【Cleft】  implies an opening or break wider and deeper than a 【crack】  and often in a natural structure; it may suggest a defect that is constitutional or an opening that is left by nature.

【Fissure】 does not differ materially from 【cleft】 except that it usually suggests a narrow and deep opening and does not carry so strong an implication of inherent defect. The term may denote a normal structural feature or an abnormal condition.

In extended use it usually suggests something abnormal or undesirable.

【Crevasse】 is applied generally and usually in its extended use to a 【fissure】 or 【cleft】 that is broad and deep, but is particularly applicable to a deep break in the surface of a glacier or a wide breach in a levee.

【Crevice】 and 【cranny】 apply especially to a space made by a break or 【crack】 (as in a wall or a cliff) that forms a place for dirt to gather or for plants to root and grow.

【Cranny】  often ( 【crevice】 occasionally) conveys so strongly the notion of an obscure, remote, or hidden nook that it loses completely all suggestion of a mode of formation.

【Chink】 implies a small break or hole sufficient for one to see through or for something to come through.