10 FREQUENTLY ASKED QUESTIONS ABOUT ROCKS AND ROCK CYCLE

10 FREQUENTLY ASKED QUESTIONS ABOUT ROCKS AND ROCK CYCLEMADE BY: FATEH ALI MEHDICLASS: VIII-FHow are rocks formed or made?Rocks can lithify from sediments, solidify from melt, precipitate out of saturated solutions, or metamorphose from other rock types. The first rocks on Earth were igneous rocks, formed from the cooling of molten material on the surface.Rocks are categorized into three distinct typesbased on their method of formation. The three types areigneous, sedimentary, and metamorphic.

What is the difference between a rock and a mineral?

Amineralis a naturally-occurring inorganic (there are some exceptions to this) crystalline solid (though mercury is regarded as a mineral) with a specific chemical composition and a characteristic internal regular geometric arrangement of atoms, sometimes expressed as natural crystal faces.Arockis an aggregate of one (such as quartzite) or more (such as granite) mineral particles formed through either crystallization of molten magma (igneous rocks), settling of particles (sedimentary rocks), or reheating and pressure applied to pre-existing rocks (metamorphic rocks), with no set chemical composition or atomic structure.

What is the relationship between sedimentary metamorphic and igneous rocks and how do they change?

Sedimentary rockis formed when sediment (sand, mud, clay, and other small rock particles) is transported by wind or water to a point of rest, where it is compressed to extreme pressures from further overlying sediments over long periods of time and the gaps between the small particles are cemented together by mineral solutions. Exposed sedimentary rock undergoes weathering by a number of means, and the resultant particles may find a point of quiet deposition and become new sedimentary rock. Igneous rockis nothing more, and nothing less, than cooled magma, either extruded or erupted on the surface (extrusive igneous rocks), or slowly cooled underground (intrusive igneous rocks). You do not find fossils within igneous rock because organic matter would be unlikely to survive the temperatures of molten rock. Igneous rocks eventually weather into smaller particles which can be transported by nature and deposited in a sedimentary basin to eventually form sedimentary rock. Igneous rock can also be sub ducted at plate boundaries, remolded, and become a new igneous rock.Metamorphic rockused to be sedimentary or igneous (or even a different kind of metamorphic), but has changed its appearance and/or mineral composition over time through extreme heat and pressure. Metamorphic rock can be formed from heat and pressure at depth, through pressures from continental collisions, or from contact of a parent rock with an igneous intrusion (called contact metamorphism). Often this kind of rock looks layered as the minerals flatten and group together at right angles to the directional force of pressure, in a banding called 'foliation'. Fossils within metamorphic rock are extremely rare, as the heat and pressure will usually remove the fossil record from previously sedimentary rock. Metamorphic rock may melt and become igneous rock, or it may become exposed at the surface through erosion or uplift. Once exposed, it is subject to weathering and may eventually become sedimentary rock.

What is the difference between intrusive and extrusive igneous rock?

Intrusiveigneous rocks cooled below the surface of the planet, however, and generally display larger crystals due to the increased amount of time spent at mineral crystallization temperatures from the insulating effect of surrounding material.

Examples: granite, gabbro, diorite, peridotite.

ExtrusiveIgneous rocks are formed from magma at or above the surface of the planet, and generally display smaller mineral crystals, or no crystals at all, because of the rapid cooling environment in which they form. Chemically, an intrusive and extrusive rock could be identical, the only difference being the size of the mineral crystals they contain.

Examples: obsidian, rhyolite, pumice, scoria, basalt.

How does the rate of cooling of magma affect the crystal size and texture of igneous rocks?

Slower rates of cooling will create larger crystals. Rapid cooling allows little time for element accumulation in the crystal, therefore, the crystals created will be smaller.Larger, visible crystals in igneous rock indicate that the magma was slow cooling, usually at depth. Much smaller crystals in igneous rock indicate rapid cooling of lava, usually at or near the surface. Crystals in igneous rock will grow larger and have more time to accumulate material for their growth the more time they have at their crystallization temperature.

How does sedimentary rock become metamorphic rock?

Sedimentary rock becomes metamorphic rock through the addition of heat and/or pressure. Contact metamorphic rocks are those primarily transformed by close proximity to an intrusion of magma, where a recrystallization or elemental transfer can take place. Sedimentary rocks like shale can metamorphose into slate mainly through pressure and heat derived from plate collision, where the alignment of minerals is changed resulting in a foliated texture.

What are the advantages of cycle of sedimentation?

The study of cycle of sedimentation and sedimentary rock has great practical value as well. Oil and gas, our most valuable sources of energy are found in these rocks. These precious resources are becoming increasingly difficult to find, and so it's more important than ever to understand how sedimentary rocks which is known as sedimentation cycle. As oil and gas decline in abundance, coal which is a distinct type of sedimentary rock will be use increasingly to generate energy. Another important energy source that may accumulate in sedimentary rock is uranium, which is for nuclear power. Phosphate rock used for fertilizer is sedimentary, as is much of the world's iron ore. Knowing how these kinds of sediment form or sedimentation cycle can help us to find and use these limited resources.

What are some examples of sedimentary rocks?

ConglomerateDiatomiteRock saltRock GypsumCoquinaAsphalt rockAlabasterGreywackeTravertineBanded ironGritstone

OrthoquartziteRadiolariteLigniteMarlDolostoneFlintChertIronstoneBrecciaShaleSandstoneLimestoneSiltstoneMudstoneChalkClay stoneItacolumiteBituminous coalOoliteOil shale

The following are examples of sedimentary rocks:

How does foliation occur?

Foliation happens when a rock is compressed from one direction and partially recrystallizes. This causes crystals of minerals like mica and chlorite to grow perpendicular to the direction of the force, and gives the rock a banded appearance.

Foliation not related to layering, though if a sedimentary rock with the right mineral makeup is metamorphosed, it may take on a foliated appearance. In this case, however, the orientation of the foliation is usually at a different angle than the original layering.

The end result of foliation is that the rock is so heavily compressed that the minerals actually rearrange themselves in response to the pressure being exerted on the rock. Sometimes this even causes reactions that form new minerals.

How is the age of a rock or rock layer determined?

A sedimentary rocks age can be estimated (relative age) by index fossils that may be present in the rock. Certain fossils only appear in rocks from a certain geologic age. This method is known as 'relative dating' and the age is called the 'relative age'. The 'absolute' geologic age of the strata which bear the index fossils has been determined by the radiometric age of igneous intrusions which are relative to the layers of sedimentary rock, according to the Law of Superposition and the Law of Horizontality. For igneous and metamorphic rock, age is determined primarily by radiometric dating based on decay of isotopes found within the rock. For some igneous rocks, the age of the rock is known precisely from historical records correlating to its formation.