Geology: the science of rocks and minerals

Geodes

Geology: The Science of Rocks and MineralsGeodes look like ordinary rocks on the outside but can be spectacular inside!

Fluorescent Minerals

Geology: The Science of Rocks and MineralsFluorescent Minerals and rocks glow with spectacular colors under ultraviolet light.

Tumbled Stones

Geology: The Science of Rocks and MineralsTumbled Stones are rocks that have been rounded, smoothed and polished in a rock tumbler.

Quartzite

Geology: The Science of Rocks and MineralsQuartzite a nonfoliated metamorphic rock composed almost entirely of quartz.

Trap Rock

Geology: The Science of Rocks and MineralsTrap Rock is a name applied to any dark-colored igneous rock used to produce crushed stone.

Difficult Rocks

Geology: The Science of Rocks and MineralsDifficult Rocks Elementary students find lots of rocks that you will not be able to identify.

Sand Grains

Geology: The Science of Rocks and MineralsA Grain of Sand Gallery of sand grains through a microscope by Dr. Gary Greenberg.

Geology Tools

Geology: The Science of Rocks and MineralsGeology Tools – Hammers, field bags, hand lenses, maps, hardness picks, gold pans.

Geology Dictionary

Geology: The Science of Rocks and MineralsGeology Dictionary – contains thousands of geological terms with their definitions.

Lapis Lazuli

Geology: The Science of Rocks and MineralsLapis Lazuli – a metamorphic rock and the most popular blue opaque gemstone in history.

Shale

Shale The rock that is quickly transforming the energy industry.

Mariposite

Mariposite – a name used for green chromium-rich micas and certain rocks colored by them.

Sand

Sand is a diverse material. This gallery includes photos of sand from around the world.

Don*t Go To Jail

Rock Collectors must know the rules before removing rocks from public and private property.

Charoitite

Charoitite – a purple metamorphic rock dominated by the mineral charoite. It is used as a gem.

Hardness Picks

Hardness Picks – Test for hardness with precise and easy-to-use hardness picks.

Rock Tumbling

Rock Tumblers – All about rock tumblers and rock tumbling. Read before you buy a tumbler.

Rock Art

Rock Art People have been producing rock art for thousands of years. A world-wide collection.

Siltstone

Siltstone is a sedimentary rock composed mainly of silt-sized particles.

Coquina

Coquina – A porous limestone composed almost entirely of fossil debris.

Rock-Forming Minerals

Rock-Forming Minerals – most of Earth*s crust is made up of a small number of minerals.

Uses of Granite

Uses of Granite The rock used everywhere from the kitchen to the facing stone of skyscrapers.

Unakite

Unakite is a metamorphosed granite composed of green epidote and pink orthoclase.

Rocks on Mars

Rocks on Mars Many of the rocks found on Mars are not very different from Earth rocks.

Gifts That Rock

Gifts That Rock – What are the most popular gift items in the Geology.com store?

Caliche

Caliche is a lithified layer in soil or sediment. It is considered to be a sedimentary rock.

Hand Lens

Hand Lens A 10-power folding magnifier in a metal case. A frequently used lab and field tool.

Oil Sands

Oil Sands contain oil in the form of bitumen – a major oil resource that can be difficult to produce.

Forensic Geology

Forensic Geology My students come to class thinking that dirt is dirt and sand is sand…

Azurite Granite ?

Azurite Granite? Found at the base of K2, the second highest mountain in the world.

Soapstone

Soapstone is a talc-rich rock with properties that make it suitable for a variety of projects.

Dacite

Dacite – a light-colored extrusive igneous rock intermediate between rhyolite and andesite.

Limestone

Limestone A versatile rock used in cement, food, paint, paper, drugs, concrete & more!

Chalk

Chalk is a variety of limestone formed from fine-grained marine sediment known as ooze.

Diabase

Diabase – the rock selected for Stonehenge and transported 240 miles in 2100 BC.

Rock identification and classification

The study of geology is the study of the Earth, and so is ultimately the study of rocks. Geologists define a rock as:

A bound aggregate of minerals, mineraloids, or fragments of other rocks. Geology: The Science of Rocks and Minerals Chert

The use of the word 'bound' means that a rock must have structural integrity, e.g. an aggregate of sand does not become a rock until the grains are bound together. Typical binding agents are very fine grained minerals (e.g. calcite, clay) or mineraloids (e.g. chert, glass), though in some rock types the crystals are intergrown and no binder is required.

Classification

There are three major groups of rocks:

  1. Igneous rocks are those that have formed by the cooling and crystallisation of magma, either at the Earth's surface or within the crust;
  2. Sedimentary rocks are those that have formed when eroded particles of other rocks have been deposited (on the ocean floor, stream/lake beds, etc) and compacted, or by the precipitation of minerals / mineraloids from water;
  3. Metamorphic rocks are those that have formed when existing rocks have undergone pressure and / or temperature changes so that their original mineralogy has been changed.

Each of these rock groups contains many different types of rock, and each can be identified from its physical features.

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Being able to describe and name rocks is one of the fundamental skills of a geologist. Important information regarding the nature of rocks is communicated through concise, accurate descriptions. This information allows the geologist to identify the rock, and, in the process, to learn about its history and the geological environment in which it was formed.

A knowledge of field relationships between different rock units is fundamental to the study of rocks. It is gained from mapping and observing rocks in the field.

In depth analysis of rocks using a microscope or sophisticated analytical laboratory equipment provides important information on their composition. In between these extremes is the observation and description of hand specimens.

The term hand specimen refers to an easily manageable piece of rock that can be picked up and easily transported back to the geologist's base for further investigation.

Methodology

Rock identification is a systematic process, requiring concise, accurate descriptions of physical characteristics. This process is called petrography.

Geologists use petrographic descriptions to communicate the essential features of rocks in writing (with illustrations / photographs if appropriate). Petrographic descriptions also summarise these characteristics for future reference.

They should contain sufficient information to allow identification of the rock.

Rock (geology)

Naturally occurring mineral aggregate
“Rocks” and “Stone” redirect here. For other uses, see Rock (disambiguation) and Stone (disambiguation).

The Grand Canyon is an incision through a number of layers of sedimentary rocks.

A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition and the way in which it is formed. Rocks are usually grouped into three main groups: igneous rocks, metamorphic rocks and sedimentary rocks. Rocks form the Earth's outer solid layer, the crust.

Igneous rocks are formed when magma cools in the Earth's crust, or lava cools on the ground surface or the seabed.

The metamorphic rocks are formed when existing rocks are subjected to such large pressures and temperatures that they are transformed—something that occurs, for example, when continental plates collide.

The sedimentary rocks are formed by diagenesis or lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks.[1]

The scientific study of rocks is called petrology, which is an essential component of geology.[2]

Classification

See also: Formation of rocks
Rock outcrop along a mountain creek near Orosí, Costa Rica.

Rocks are composed of grains of minerals, which are homogeneous solids formed from a chemical compound arranged in an orderly manner.[3][page needed] The aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which it was formed.

Most rocks contain silicate minerals, compounds that include silicon oxide tetrahedra in their crystal lattice, and account for about one-third of all known mineral species and about 95% of the earth's crust.[4] The proportion of silica in rocks and minerals is a major factor in determining their names and properties.[5]

Rocks are classified according to characteristics such as mineral and chemical composition, permeability, texture of the constituent particles, and particle size.

These physical properties are the result of the processes that formed the rocks.[6] Over the course of time, rocks can transform from one type into another, as described by a geological model called the rock cycle.

This transformation produces three general classes of rock: igneous, sedimentary and metamorphic.

Those three classes are subdivided into many groups. There are, however, no hard-and-fast boundaries between allied rocks.

By increase or decrease in the proportions of their minerals, they pass through gradations from one to the other; the distinctive structures of one kind of rock may thus be traced gradually merging into those of another.

Hence the definitions adopted in rock names simply correspond to selected points in a continuously graduated series.[7]

Igneous rock

Main article: Igneous rock
Sample of igneous gabbro

Igneous rock (derived from the Latin word igneus, meaning of fire, from ignis meaning fire) is formed through the cooling and solidification of magma or lava. This magma may be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.

Igneous rocks are divided into two main categories:

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  • Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust. A common example of this type is granite.
  • Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt.[6]

The chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowen's reaction series. Most major igneous rocks are found along this scale.[5]

About 65% of the Earth's crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalt and gabbro, 16% are granite, and 17% granodiorite and diorite. Only 0.

6% are syenite and 0.3% are ultramafic. The oceanic crust is 99% basalt, which is an igneous rock of mafic composition. Granite and similar rocks, known as granitoids, dominate the continental crust.

[8][9]

Sedimentary rock

Main article: Sedimentary rock
Sedimentary sandstone with iron oxide bands

Sedimentary rocks are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms[10] or as chemical precipitates and organic growths in water (sedimentation). This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation at moderate temperatures and pressures (diagenesis).

Before being deposited, sediments are formed by weathering of earlier rocks by erosion in a source area and then transported to the place of deposition by water, wind, ice, mass movement or glaciers (agents of denudation).[6] About 7.

9% of the crust by volume is composed of sedimentary rocks, with 82% of those being shales, while the remainder consists of limestone (6%), sandstone and arkoses (12%).[9] Sedimentary rocks often contain fossils.

Sedimentary rocks form under the influence of gravity and typically are deposited in horizontal or near horizontal layers or strata, and may be referred to as stratified rocks.[11]

Metamorphic rock

Main article: Metamorphic rock
Geology: The Science of Rocks and Minerals Metamorphic banded gneiss

Metamorphic rocks are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism, meaning to “change in form”. The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization.[6] The temperatures and pressures required for this process are always higher than those found at the Earth's surface: temperatures greater than 150 to 200 °C and pressures of 1500 bars.[12] Metamorphic rocks compose 27.4% of the crust by volume.[9]

The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation.

Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant, and temperature plays a smaller role. This is termed burial metamorphism, and it can result in rocks such as jade.

Where both heat and pressure play a role, the mechanism is termed regional metamorphism. This is typically found in mountain-building regions.[5]

Geology: The Science of Rocks and Minerals

A few days ago, my birdwatching daughters started to develop a sudden interest in rocks and minerals.

I’m far from an expert in geology, so we set off to see what we could learn together. There are a ton of great resources that I’ll link to later on, but today I just want to share a few interesting highlights and surprising facts that we discovered about the hardest of sciences. (That’s the last bad joke for this episode.).

Rocks vs. Minerals vs. Crystals

The first thing we wondered is – what’s the difference between a rock, a mineral, and a crystal? It turns out that a “rock” is made up of two or more different kinds of mineral particles.

So if you take a piece of granite (a rock) and look at closely, you’ll see that it’s made up of a bunch of tiny mineral particles, mostly quartz, mica, and feldspar, with a few other minerals mixed in.

 

If you have a pure mineral, such as a big hunk of quartz, it will typically be in a crystal shape. That’s because minerals are all made of the same kind of molecule, and molecules that are all the same, have a tendency to line up in nice organized patterns. Our chunk of quartz is made up of a bunch of Silicone dioxide molecules (SiO₂) lined up in a trigonal crystal shape. 

So to summarize, rocks are made up of two or more different kinds of mineral particles, while crystals are formed by single minerals. 

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The Rock Cycle

The Basics of Rocks and Minerals and Polar Geology

Minerals, quite simply, are the building blocks for making rocks, and a rock is made up of one or more minerals.

When you look at a rock and see different colors, those colors are minerals that make up that specific rock.

There are over 3,000 named minerals; however, there are really only about 30 minerals that people who are not geologists will come across or need to concern themselves with.

There are four criteria that must be met in order for something to be called a mineral:

  1. Not formed from the remains of plants or animals; that is, inorganic
  2. Naturally occurring, not man-made
  3. Has the same chemical makeup wherever it is found (Ex: Quartz is always SiO2)
  4. Has a crystalline structure, which means that it has a specific repeating pattern of atoms.

If all four of the criteria are not met, the substance is not a mineral. Therefore, “minerals” made in a lab are not true minerals because they did not occur naturally.

Here are a few tests that geologists rely on to identify what minerals they are looking at.

Color – Color is a very common way to try to identify a mineral; however, it should not be used on its own. Because any mineral can be any color, you cannot use color alone to identify a mineral. Color can merely help you. (Or, sometimes, confuse you!)

Shape

Geology 101

You see Abe Lincoln's face. The Grand Canyon. An awesome ancient pyramid. A geologist sees granite, volcanic rock, limestone, and the Earth over millions of years. In other words, rocks.

You can't throw a rock without … hitting another rock. They're everywhere. Rock creates and shapes the Earth's landscape. It forms our magnificent mountains, shapes the deepest oceans, and safely separates us from the boiling magma beneath our feet! (Okay, technically magma is uber-hot liquid rock. But you don't want to stand on it.)

Water, wind, earthquakes, cold, and heat scour, fracture, move, or melt rock. Rock is continuously being changed, rebuilt, or recycled by the forces of the Earth.

Granite, limestone, marble, and sandstone are examples of kinds of rock. Geologists divide rocks into three large groups: igneous, metamorphic, and sedimentary. Lava or magma form igneous rock. Changes in pressure or heat create metamorphic rock. Water and wind create sedimentary rock. (Each rock group includes hundreds of different kinds of rocks.)

Classroom Geology | Fisher Scientific

View the brilliant light of the sun safely with this wooden, folded-path Keplerian telescope.

12 Samples that the whole room can see.

12 giant fossils show incredible details.

Used for hardness testing of rocks and minerals.

Excellent introduction to minerals.

Dig into some serious fun with these fascinating collection kits.

40 large, carefully cut, and selected specimens.

Learn about and classify fossils that are many hundreds of millions of years old.

For use in hands-on exploration of rocks and minerals in classroom setting. EISCO; Basic Rocks and Minerals Kit contains 40 specimens and specimen key.

Provides all 10 minerals used in Mohs Scale of Comparative Hardness.

Follow step-by-step instructions to easily learn the properties of minerals.

Journey to the center of the Earth.

Learn the characteristics of rocks including texture, grain size, and mineral content.

Use investigative processes to learn geological content.

Phyllite Specimen for demonstrations of metamorphic properties, such as glossy sheen and dense, foliated minerals.

For use as tool to explain specific gravity to students – EISCO Galena Mineral Specimen is used in classroom identification labs and exercises, correlates well to Next Generation Science Standards Evidence Statements.

Identify forms, colors, refraction and fossil inclusions.

For use in comparing with other igneous rocks, particularly as part of lessons on Bowen's reaction series. EISCO Peridotite Specimen (Igneous Rock) is iron-rich ultramafic rock, with chemistry that suggests genesis from point deep within crust.

Reusable game reinforces the concepts of the rock cycle.

Anthracite Coal is formed in anoxic environments from compressed organic matter, and is used worldwide as fuel source.

Pumice is formed quickly during volcanic eruptions around pockets of air within lava.

Excellent way to illustrate various structures related to fault planes and fractures.

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