Shale is metamorphosed into three rock types: (1) a banded gneissic rock; (2) a rock with small mica crystals with a shiny aspect; (3) a very shiny rock with large mica crystals; and (4) a dull slate with cleavage. Which of the following lists these rocks in order of increasing metamorphic grade?
a. 1, 2, 3, 4
b. 4, 3, 2, 1
c. 2, 3, 4, 1
d. 4, 2, 3, 1
e. 3, 2, 4, 1

d. 4, 2, 3, 1

Explanation:

Shale is a type of sedimentary rocks, which is characterized by it fine-grained, fissile and laminated nature. It is formed through the mixing of silt and mineral particles often referred to as mud.

Shales are metamorphosed through the heat and pressure, into a hard fissile metamorphic rock known as SLATE. SLATE is characterized by it fine-grain nature with well developed rock cleavage or salty cleavage. Then it metamorphose to PHYLLITE, which is also characterized by its fine-grained mica flakes, and it contains quartz, sericite micas and chlorite. After PHYLLITE, the shale metamorphosed to SCHIST; identified by its coarse grain nature, with mica crystals that are large enough, to unaided eyes. From there, Shale metamorphosed finally to GNEISS; a branded rock, characterized by its medium to coarse grain nature, with poorly developed cleavage.