Metamorphic, Igneous, and Sedimentary Rocks and Their

Metamorphic, Igneous, And Sedimentary Rocks and Their Application to Planets in the Solar System

The objective of this study is to examine metamorphic, igneous, and sedimentary rocks and their application to planets in the solar system.

There are reported to be three primary classes of rocks, which are classified according to their origination. The three rock types are metamorphic, igneous, and sedimentary rocks. Igneous rocks are formed when bodies of magma cool. As time passes and the rocks undergo process due to various weather cycles the igneous rocks erode and the particles and chemicals, which settle into beds, become compressed or cemented forming into what are known as sedimentary rocks. In the event igneous rocks are buried and then undergo a high state of heating and compression they form into what are known as metamorphic rocks. Eventually, the rocks undergo heat and compression and then melt with the molten rock forming another igneous rock in what is referred to as the rock cycle. Rocks may be turned from one type of rock into another rock. For example, it is reported that a sedimentary rock "such as sandstone can be weathered and eroded and those fragments might eventually end up as part of a shale, a different sedimentary rock." (Rocks & Other Mineral Sources, 2012) The following illustration shows the rock cycle that the three primary rocks types undergoes in the changing of rocks from one type to the other.

Figure 1

Rock Cycle

Source: Nelson (2012)

I. Rock Classes and Types of Rocks

There are two classes of rocks that are formed from magma including: (1) plutonic or intrusive rocks; and (2) Volcanic or extrusive rocks. The types of rocks that are formed from the consolidation of sediments include: (1) biochemical sedimentary rocks; (2) Clastic sedimentary rocks; and (3) evaporative sedimentary rocks. Metamorphic rocks or those formed from heat and pressure include such as: (1) Geniss; (2) marble; (3) quartzite; (4) phyllite; (5) schist; (6) serpentine; (7) slate; and (8) soapstone. The following illustration shows the development or formation of slate.

Figure 1

Formation of Slate

Source: Nelson (2012)

Specific igneous rocks include in the intrusive class those of: (1) granite; (2) quartz; (3) potassium; (4) sodium-rich feldspar; (5) mica gabbro; (6) dark rock of calcium-rich feldspar; (7) pyroxene perodotite; and (8) dark rock, mostly olivine. Igneous rocks of the extrusive type include basalt, which is a fine-grained equivalent of a gabbro. Two common terrestrial sedimentary rocks are reported to be those of sandstone and limestone. Sandstone is formed "from compressed sand grains" and limestone is "produced when deposits of calcium carbonate (CaCO3) precipitate out of solution in water. Limestone's formation is similar to the "mineral bathtub rings left when water evaporates out of a tub." (Rocks & Other Mineral Sources, 2012)

II. Planets and Rock Classes

Sedimentary rocks are not found on the moon since it is reported to lack "the wind-and-water driven erosive processes that create and deposit sediments." (Zooniverse, 2012) The surface of Mars however, "experiences lots of wind erosion and it appears to have been subjected to significant water erosion in the past." (Zooniverse, 2012) Earth is reported as a "restless planet" and there are very few rocks on earth that have not undergone changes over the 4.5 billion years of time geologically speaking. The oldest earth rocks are reported to be some genisses or highly metamorphosed granites which are located in Canada and which are stated to have formed approximately four billion years ago. Other planets in the solar system do not experience the same level of change as does the earth so the rocks on other planets tend to be much older than rocks on the earth. The oldest moon rocks are reported as being approximately 4.4 to 4.5 billion years old and this is also held to be the moon's age. Meteorites found on Mars are reported to be approximately 4.5 billion years old and this is stated to indicate that "the Martian surface has not been recycled by plate tectonics as the Earth's surface has been." (Zooniverse, 2012) Metamorphic rocks, which form when igneous or sedimentary rocks undergo conditions of heat, pressure or hot water that contains acidic solutions or dissolved mineral which changes the texture of the minerals and results in the creation of new types of rock are generally formed at a very deep place in the earth and erosion of movements within the planet uncover the rocks. This rock, while occurring on the moon is much rare and is reported to be formed through events of impact. When the lunar rocks of this type are examined in the lab the evidence shown is that referred to as "shock metamorphism." (Zooniverse, 2012)

III. Minerals and Rock Formation

Three minerals are important to understand in the study of rock formation. Those are stated as follows:

(1) Clay Minerals - Clay minerals are sheet silicates, thus they have a crystalline structure that allows them to break easily along parallel sheets. Clay minerals form by alteration of other minerals during the process of chemical weathering (alteration under conditions present near the Earth's surface). Thus clay minerals are primary constituents of soils and are also found in the sedimentary rock known as shale or mudstone;

(2) Calcite - chemical formula CaCO3 (calcium carbonate). Calcite is easily dissolved in water under slightly acidic conditions. Thus calcite can be precipitated directly from water. Organisms can extract the Calcium and Carbonate ions from water to precipitate their shells. Thus calcite is a primary constituent of chemical and biochemical sedimentary rocks; and (3) Quartz - Chemical Formula SiO2. - Quartz is one of the primary minerals that originally forms by crystallization from a melt in igneous rocks. Although quartz is formed at relatively high temperatures it is stable (does not break down or alter) at conditions present near the Earth's surface. Thus quartz is a primary constituent of sand, soil, and sedimentary rocks called sandstones. (Nelson, 2012)