Question

How do you easily tell the difference between igneous, metamorphic, and sedimentary?

Answer 1

Classification of rocks is based on origin: Igneous rocks are formed by solidification of magma/lava
(freezing) or by accumulation of fragments ejected during volcanic eruptions. Sedimentary rocks are
formed by the deposition and subsequent aggregation of rock or mineral fragments produced by erosion
and transported by gravity, wind, ice or water. Some sedimentary rocks may also form by precipitation of
minerals from the dissolved elements present primarily in seawater. Metamorphic rocks are formed when
existing sedimentary or igneous rocks are subjected to changes (primarily increases) in temperature,
pressure or stress, which cause the mineral grains originally present to reorient, recrystallize or be replaced
by new minerals, stable under the new conditions.

Igneous rocks are composed of hard minerals (H ˜ 6-7), primarily feldspar, sometimes quartz, and a dark
mafic mineral, either olivine, pyroxene, hornblende or biotite (the only soft mineral in igneous rocks).
Mineral grains usually have good crystal shapes, and different mineral types are randomly distributed
through the rock, not in layers. Grain size is quite variable.

Sedimentary rocks are aggregates of transported particles or chemical precipitates composed of calcite,
dolomite or gypsum. Some may contain fossils. Clastic sedimentary rocks are composed primarily of
quartz, feldspar and clay minerals. The mineral grains are often rounded, and dark minerals are rare.
Sedimentary rocks often have conspicuous layering, or bedding.

Metamorphic rocks may be distinguished by their foliation, which is a parallel alignment of platy mica
grains or of light and dark layers. When pure quartz or pure calcite rocks are metamorphosed the mineral
grains become coarse and polygonal in shape giving the rock a “sugary” texture.

Answer 2

Thank you

Answer 3

your welcome!(: