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Chalk is a soft, white, powdery limestone consisting mainly of fossil shells of foraminifers
From old English cealc chalk, lime, plaster; pebble, from Greek khalix small pebble, in English transferred to the opaque, white, soft limestone
Fine Grained Rock, Opaque Rock
Phyllite is a fine-grained metamorphic rock with a well-developed laminar structure, and is intermediate between slate and schist rocks
From Greek phullon leaf + -ite1
Coarse Grained Rock, Fine Grained Rock, Medium Grained Rock, Opaque Rock