Tahlequah Rock Earthcache EarthCache

Sedimentary Rocks :

Are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or minerals to precipitate from a solution.

Metamorphic:

Arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (1500 bars), causing profound physical and/or chemical change.

Igneous:

(Derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava.

What are Sedimentary Rocks?

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2)chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3) organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris. A brief descriptions of some common sedimentary rock types are shown below.

Types of Sedimentary Rocks:

Breccia:

Clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together.

Chert:

A microcrystalline or cryptocrystalline sedimentary rock material composed of silicon dioxide (SiO2). It occurs as nodules and concretionary masses and less frequently as a layered deposit. It breaks with a conchoidal fracture, often producing very sharp edges. Early people took advantage of how chert breaks and used it to fashion cutting tools and weapons.

Coal:

An organic sedimentary rock that forms mainly from plant debris. The plant debris usually accumulates in a swamp environment. Coal is combustible and is often mined for use as a fuel.

Conglomerate:

A clastic sedimentary rock that contains large (greater then two millimeters in diameter) rounded particles. The space between the pebbles is generally filled with smaller particles and/or a chemical cement that binds the rock together.

Dolomite:

(Known as "dolostone" and "dolomite rock") is a chemical sedimentary rock that is very similar to limestone. It is thought to form when limestone or lime mud is modified by magnesium-rich groundwater.

Flint:

Hard, tough chemical or biochemical sedimentary rock that breaks with a conchoidal fracture. It is a form of microcrystalline quartz that is typically called “chert” by geologists. It often forms as nodules in sedimentary rocks such as chalk and marine limestones.

Iron Ore:

Chemical sedimentary rock that forms when iron and oxygen (and sometimes other substances) combine in solution and deposit as a sediment. Hematite (shown above) is the most common sedimentary iron ore mineral.

Limestone:

A rock that is composed primarily of calcium carbonate. It can form organically from the accumulation of shell, coral, algal and fecal debris. It can also form chemically from the precipitation of calcium carbonate from lake or ocean water. Limestone is used in many ways. Some of the most common are: production of cement, crushed stone and acid neutralization.

Oil shale:

Is a rock that contains significant amounts of organic material in the form of kerogen. Up to 1/3 of the rock can be solid organic material. Liquid and gaseous hydrocarbons can be extracted from the oil shale but the rock must be heated and/or treated with solvents. This is usually much less efficient than drilling rocks that will yield oil or gas directly into a well. The processes used for hydrocarbon extraction also produce emissions and waste products that cause significant environmental concerns.

Rock Salt:

Is a chemical sedimentary rock that forms from the evaporation of ocean or saline lake waters. It is also known by the mineral name "halite". It is rarely found at Earth's surface, except in areas of very arid climate. It is often mined for use in the chemical industry or for use as a winter highway treatment. Some halite is processed for use as a seasoning for food.

Sandstone:

Is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris. Environments where large amounts of sand can accumulate include beaches, deserts, flood plains and deltas.

Shale:

Is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.

Siltstone:

Is a clastic sedimentary rock that is made up of clay-size (less then 1/256 millimeter in diameter) weathering debris. It typically breaks into thin flat pieces.

Types of Weathering

Types of Weathering

Is the breaking down of rock , soil and minerals as well as artificial materials through contact with the Earth’s atmosphere, biota and waters. Weathering occurs "with no movement" , and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other location. 1. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure. 2. Chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals.

Hardness of the rocks:

One of the most important tests for identifying mineral specimens is the Mohs Hardness Test. This test compares the resistance of a mineral to being scratched by ten reference minerals known as the Mohs Hardness Scale (see Table 1). The test is useful because most specimens of a given mineral are very close to the same hardness. This makes hardness a reliable diagnostic property for most minerals.

Friedrich Mohs, a German mineralogist, developed the scale in 1812. He selected ten minerals of distinctly different hardness that ranged from a very soft mineral (talc) to a very hard mineral (diamond). With the exception of diamond, the minerals are all relatively common and easy or inexpensive to obtain.

What is Mohs Hardness Scale?

Definitions

Arkose:

Is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose. Quartz is commonly the dominant mineral component, and some mica is often present.

Chemical sedimentary rocks :

Chemical sedimentary rock forms when mineral constituents in solution become supersaturated and inorganically precipitate. Common chemical sedimentary rocks include oolitic limestone and rocks composed of evaporite minerals such as halite (rock salt), sylvite, barite and gypsum.

Clasts:

A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, and in sediment deposits.

Clastic sedimentary rocks:

Clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on grain size, clast and cementing material (matrix) composition, and texture.

Conchoidal fracture:

Describes the way that brittle materials break or fracture when they do not follow any natural planes of separation. Materials that break in this way include quartz, flint, quartzite, and other fine-grained or amorphous materials with a composition of pure silica, such as obsidian and window glass.

Grus:

Is an accumulation of angular, coarse-grained fragments (particles of sand and gravel) resulting from the granular disintegration (caused by chemical weathering and mechanical weathering) of crystalline rocks generally in an arid or semiarid region. Grus sand, when cemented into a sandstone, will form an arkose.

Mechanical weathering:

Mechanical weathering is the set of various processes of weathering that break apart rocks into particles (sediment).

There are five major mechanisms of mechanical weathering:

Abrasion is the grinding action of other rock particles due to gravity or the motion of water, ice or air. 2.Crystallization of ice (frost shattering) or certain minerals such as salt (as in the formation of tafoni) can exert enough force to fracture rock. 3.Thermal fracture is the result of rapid temperature change, as by fire, volcanic activity or day-night cycles (as in the formation of grus), all of which rely on the differences in thermal expansion among a mixture of minerals. 4.Hydration shattering may strongly affect clay minerals, which swell with the addition of water and force openings apart. 5.Exfoliation or pressure release jointing results from the stress changes as rock is uncovered after its formation in deep settings.

Organic sedimentary rocks:

Abrasion is the grinding action of other rock particles due to gravity or the motion of water, ice or air. 2.Crystallization of ice (frost shattering) or certain minerals such as salt (as in the formation of tafoni) can exert enough force to fracture rock. 3.Thermal fracture is the result of rapid temperature change, as by fire, volcanic activity or day-night cycles (as in the formation of grus), all of which rely on the differences in thermal expansion among a mixture of minerals. 4.Hydration shattering may strongly affect clay minerals, which swell with the addition of water and force openings apart. 5.Exfoliation or pressure release jointing results from the stress changes as rock is uncovered after its formation in deep settings.

Organic sedimentary rocks:

The sediment in an organic sedimentary rock is made of fossils! The hard parts of animals, such as bones and shells, can become cemented together over time to make rock. Usually the bones and shells are made of calcite, or similar minerals, and the organic rock that is made from them is called limestone.

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