Theory question 306
Rocks(a) List three types of sedimentary rocks classified according to their mode of formation. (b) Name the rocks that are formed when the following undergo metamorphism: (i) granite; (ii) clay; (iii) shale; (iv) limestone (c) Outline four differences between sedimentary and metamorphic rocks.
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(a) Mechanically formed (clastic) rocks, e.g. sandstone, shale; organically formed rocks, e.g. limestone, coal, chalk; chemically formed rocks, e.g. rock salt, gypsum, potash.
(b)(i) Granite - gneiss; (ii) clay - slate; (iii) shale - slate (or schist); (iv) limestone - marble.
(c) Sedimentary rocks are formed from deposited sediments, metamorphic rocks from existing rocks changed by heat and/or pressure; sedimentary rocks are in layers (strata), metamorphic rocks are banded or foliated; sedimentary rocks may contain fossils, metamorphic rocks rarely do; sedimentary rocks are usually soft and porous, metamorphic rocks hard, compact and non-porous; sedimentary rocks form at the surface, metamorphic rocks deep in the crust.
Each difference should compare both rocks.