What is Sand? copy

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Poliou Potami Beach, Karpathos Island, Greece | Photo by Leo Kenney

Sand

Sand is a specific size of loose grains of natural minerals, rocks, and organic remains.

Most people think of sand as the granular material at the beach or on a desert. They have a generalized definition for “sand”. However, to geologists, “sand” is defined as a sediment in the size range of 0.063 to 2 mm. And within that scale, “sand grains” range from very coarse (2 mm) to very fine (0.063 mm). (Larger than “sand” would be pebbles, cobbles and boulders. Finer than “sand” would be silt and clay.)

Sand is formed in three ways. The vast abundance of sand is formed by the breakdown of pre-existing rocks by weathering and erosion. The breakdown produces two products: mineral grains and lithic or rock fragments. Sand can also be formed from biogenic material such as the skeletal remains of marine organisms. Lastly, some sand grains are formed by chemical reactions.

Sand is a specific size of loose grains of natural mineral, rocks, and organic remains. One definition of sand size is from .0625 mm to 2 mm. (Sand Dunes, Colorado, USA)

Sand Characteristics

A sand sample can be described in terms of grain size, color, composition, morphology (angularity and shape), and surface texture. Grain size is a result of several factors, including composition, durability, severity of weathering conditions, transport distance from its site of origin, and physical sorting by wind and/or water currents.

Left to right

Row 1: 1. Marquette Park Beach, Lake Michigan, Gary, IN, USA; 2. Navakshott, Trarza Region, Mauritania; 3. Ocean Cay, Bimini Island, Bahamas; 4. Foreman Arch, Devils Backbone, OR, USA;

Row 2: 1. Shipwreck Beach, Zakynthos Island, Greece; 2. Mackenzie River, Northwest Territories, Canada; 3. Kaihalulu Beach, Hana, Maui, HI, USA; 4. Flagler Beach, FL, USA;

Row 3: 1. Broad Cove, Cape Breton, Nova Scotia, Canada; 2. Isla Verde Beach, Calle Gardenia, Carolina, Puerto Rico; 3. Cedar Creek Reservoir, AL, USA; 4. Green Sands Bay, Hawaii, HI, USA;

Row 4: 1. Vatnajökull National Park, Iceland; 2. Khongoryn Els Singing Dunes, Gobi Desert, Mongolia; 3. Taketomi Island, Okinawa, Japan; 4. White Sands, Tularosa Valley, NM, USA

Grain Size

In the images of Very Coarse and Fine sand, notice the scale bar in the lower left corner. The bar represents 2 mm. Notice how many grains of the very coarse and fine sands fir within the 2 mm scale bar.

Very Coarse Sand. (Wellfleet, Massachusetts, USA)

Fine Sand. (Great Erg, Tunisia)

Grain Roundness

The roundness of sand grains can provide clues to their history of transport from its original source. During sediment transport, individual grains will repeatedly come into contact with other grains (and other objects too). During this transport, the sharp edges of the grains tend to be chipped off first. Progressive rounding and smoothing occurs with continued transport and agitation. Thus rounding reflects the transport of the grains.

Transport and rounding can occur in rivers, by waves and currents along a coastline, or by wind in the desert. The Ice Age glaciers were also responsible for transporting tons of material from their original source locations.

Angular grains of clear quartz and pink to orange feldspar are remnants of granite bedrock. (Masai Mara National Reserve, Kenya.)

Angular grains of mollusks and barnacles are found on the shore of the landlocked, highly saline Salton Sea. (Salton Sea, California, USA.)

Rounded quartz grains in the Syrian Desert are iron stained. Desert sands are often frosted from abrasion.(Jabal Qasiyun area, Syria.)

Rounded grains of echinoderm spines, mollusks, and other marine organisms have been smoothed in a high energy beach environment. (Playa La Posita, Puerto Rico.)

Sorting

Sorting. Sand tends to get sorted by size and weight as it moves. This is often seen along coastlines and in rivers. Sand that is mostly the same material with similar grain size may have travelled a long distance from its source, or its source may be mostly the same material. Sand that has a variety of materials could be an indication that it hasn’t travelled far, so its source may be close, or it may have multiple sources. Sorting combined with angularity helps us learn how grains of sand are a product of the processes of their environment. Angularity and sorting are variable based on various processes over time.

This poorly sorted sand has two sources. The fine grains originated in the mountains. The larger grains eroded off the coastal limestone cliffs. (Cala Dels Pinets, Vinaros, Spain)

This well sorted sand is the result of thousands of years of wind borne sand forming extensive dune fields. (Great Sand Dunes, Colorado)

Composition

Sand comes from the things around it. Sand can contain rocks, tiny mineral crystals, pieces of minerals, whole tiny animals, parts of animals, and fossils. It can contain bits of things made by humans too. Rock and mineral sand can help us understand the geology and mineralogy of an area.

Sand Composed of Rock

Fragments of Metamorphic rocks, such as schists and gneisses, can be recognized by their aligned layers or "fabric." The high pressure and temperature during metamorphism results in mineral grains, especially mica, becoming reoriented and layered in the rocks. The mica schist at Cape Elizabeth, Maine, has weathered from the coastal ledges. (Two Lights State Park, Cape Elizabeth, Maine, USA)

This story and the sand seem out of place. What we see if the resutl of a rock breaking down and not rocks as sand.

Fragments of sedimentary rocks are generated when pre-existing rocks weather and erode. Consider a sandstone made of quartz grains: The quartz grains in that sandstone originated elsewhere eons ago (likely in a granite), then were transported by waves or wind and eventually deposited and recemented into rock. As the sandstone breaks down again, quartz grains are once again free to roll around on the beach or blow in the desert. Sand grains can be reworked in this process, and sand grains may go through a number of cycles of erosion and re-deposition. And with each cycle the grains become rounder and rounder. This sample, Jordan Sandstone, when exposed at the surface, easily decomposes into quartz sand. (Jordan Sandstone, St, Paul, Minnesota, USA)

Sand Composed of Minerals.

Mineral sands are formed by weathering (mechanical and chemical breakdown) of igneous (plutonic or volcanic), metamorphic or sedimentary rocks. Weathering serves to free individual mineral grains or rock fragments from the parent material. A large number of minerals may occur in sand. We will describe the most common.

Quartz

Quartz is the MOST common mineral found in sand and sandstone. As a primary mineral, it is a major constituent of granitic rock and metamorphic rocks such as gneiss. As those rocks breaks down, the quartz grains remain intact over long distances and eons of time. Quartz is a very stable mineral that is resistant to chemical breakdown at the earth's surface.

Grains of quartz can be broken or abraded during transport, but with a hardness of 7 on the Mohs' scale of hardness, quartz grains remain intact over long distances and long periods of transport. Over time, quartz grains become rounder and rounder. They can be clear or cloudy; some quartz grains show reddish iron staining. (Duck Harbor, Wellfleet, Massachusetts, USA)

Mica

Mica flakes are platy in shape and may be found in sands where the local bedrock contains metamorphic rocks. There are many varieties of mica. The most common is white mica (muscovite) and brown mica (biotite). (Caption. (River Valley, Ontario, Canada))

Heavy Minerals

Swaths or waves of black to purple or pink sand on the beach or shoreline contain heavy minerals. These sands may include pink or red garnets, opaque magnetite and ilmenite, green epidote, blue sapphires, clear zircons and even flakes of gold. Heavy minerals have densities higher than quartz. The wind and waves tend to remove the less dense minerals (such as quartz) and concentrate the heavy minerals. Zircon grains are typically tiny; grains fluoresce yellow-orange under UV light. These sands are some of the most beautiful mineral sands when viewed under the microscope.

Garnet above high normal high tide line. (Orient Point, Long Island, NY, USA)

Need a better mica image (maybe) of a different mineral. We do mention “common” above, through.

Dark patterns of heavy minerals left as tide ebbs. (Fire Island, Long Island, NY, USA)

This is as far as I have gotten. Can we pick four to make them fit better.

Below, I have to bring in some of your text and create captions.

Garnet

Caption. (Plage De La Paree, Bretignolles-sur-mer, France)

Caption. (Lake Baikal, Russia)

Caption. (Madeline Island, Lake Michigan, Michigan)

Over the ages, lightning has ignited coal seams which have cooked, fused, and melted the adjacent rocks—transforming them. Visible above are examples: sandstone backed in brick-like rocks, shale that fused into a ceramic-like product and other rocks that melted and look like hardened lava or glassy slag. The clear blue/gray grains are likely Montana agates. (Collected from anthill, Yellowstone River, Terry, Montana, USA)

Grains of fine-grained igneous rock such as basalt (blue/black) are only found close to the source. Beaches around many volcanic islands are black because they are made up of basalt. The basalt in this sample is from adjacent cliffs and is mixed with fragments of barnacles and mussels. (Skarðsvík Beach, Iceland)

Feldspar

Most igneous rocks, including granites, contain feldspar as a major component and hence, feldspar grains are commonly found in sands. Feldspar grains are moderately elongated, and they may show a well-developed cleavage of near 90°.

Feldspar is technically a mineral group with varying amounts of calcium, potassium and sodium. With variations in chemistry, the grain color can be clear to cloudy, pinking, orangish, or yellowish.

The potassium feldspars (orthoclase and microcline) are most common in sands as they are chemically stable and withstand weathering. Orthoclase is pink to white. Microcline is white, pink or green. Plagioclase feldspars (albite and oligoclase) have varying proportions of calcium and sodium. These are typically colorless. (Pikes Peak, Colorado, USA)

Olivine

Olivine is a pale olive green to yellow-green mineral with a translucent luster that is commonly found in igneous rocks, and thus–sands from volcanic regions. Olivine is a mineral series with varying amounts of iron and magnesium in the crystal structure. Fayalite and forsterite are the most common members. Fayalite is iron rich and brownish-gray; forsterite is magnesium rich and olive-green to yellow-green. If you find olivine in a sample, you can be nearly certain, the region has volcanic origins. However, because olivine weathers and breaks down, it is only found where the volcanic activity is "recent." Olivine is found in basalt sands from Hawaiian sands, but not in the basalt sand beaches of Lake Superior. (Green Sand Bay, Hawaii)

Layers of dark mineral sands in an ancient cliff. (Madeline Island, Lake Superior, Michigan, USA | Kate Clover photo.)

Patterns of garnet, magnetite, epidote and quarts on the beach as the tide ebbs. (Lighthouse Beach, Coos Bay, Oregon, USA | Steven Michael photo)

Patterns of garnet, magnetite, epidote and quarts on the beach as the tide ebbs. Note the gull tracks. (Lighthouse Beach, Coos Bay, Oregon, USA | Steven Michael photo)

Caption. (Devils Backbone, Oregon, USA)

Precipitated Sands

Precipitated sands comprise the second category and are mineral grains formed from an aqueous solution. Such sands include round oolitic sands that form in the shallow waters of the Great Salt Lake, the Caribbean, off the Florida Keys and in the Arabian Sea. Borax from Death Valley, California, salt from the Dead Sea and the gypsum sands found at the White Sands desert of New Mexico are examples of evaporite deposits. Evaporites form as salt-rich bodies of saline waters evaporate, thereby becoming supersaturated and incapable of retaining the minerals in solution. It is interesting to note that the Death Valley borax and White Sands gypsum, while originally existing in solution in rather extensive bodies of water, now survive in arid conditions, a testament to the inevitability of change in the natural world.

Caption. (Antelope Island, Great Salt Lake, Utah, USA)

Do we include glauconite here? How about halite? Would Dead Sea sand with salt crystals quality?

I have Death Valley borax but its not pretty. No need for a photo of that.

Caption. (Salt, Dead Sea, Israel)

Caption. (White Sands, Tularosa Valley, New Mexico, USA)

Biogenic Sands

Biogenic sands are a third category. These are also known as "carbonate sands" as they are composed of the hard skeletal fragments of marine organisms whose body structures are made of calcium carbonate (either calcite or aragonite).

Biogenic sands are composed of whole or broken fragments of marine organisms: corals, shells (bivalves and gastropods), sea urchins, barnacles, and many others creatures. Also, some algae calcify, and their lobes contribute to sands. The grains in a biogenic sample vary from location to location and reflect the marine ecosystem and the marine organisms in that particular location. When viewed under magnification, biogenic samples are among the most interesting of sand grains.

To test for carbonates in a sand: Put a couple drops of white vinegar or other mild acid on a small amount of sand; if the sample bubbles and fizzes, that confirms it contains grains made from calcium carbonate. Rocky sands will not react with the acid.

Fragmented mollusk shells are common components of sand. The species and abundance vary with the environment. (Old-Nessebar, Black Sea, Bulgaria)

Foraminifera (forams) are single cell protists found in all marine environments. They may be particularly abundant in some areas. Forams compose much of the sand on this beach.. (Diakofti Beach, Diakofti Island, Greece)

Above: Segments of Halimeda, a calcareous green alga, are found in tropical to subtropical habitats. (Calabash Cay, Belize). Below: A branch of articulated (segment conected) red coralline algae can be found in temperate habitats.

Barnacle shells are composed of various shaped plates. Together these platesgments ……….. (Qochyax Island, Oregon, USA)

Guam sample.

Papua New Guinea sample.

Worn fragments of sea urchin spines and tests (shells) from Puerto Rico, Dominican Republic and Hawaii.

On this rocky coast, urchin spines and tests are mixed with barnacle plates, mussel shells, and grains of mica shist to form a coarse sand. The were attached to the knobs protruding from the test piece. (Dive Club Beach, Ascension Island)

Segments of the calcified green macroalgae Halimedia look like oatmeal flakes in sand samples. (Garden Key, Dry Tortugas, Florida, USA)

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Body parts are fragmented by predation, wave actions, pounding surf and other physical assaults. These pieces were excreted by a gull that had been feeding at the shore. (Plum Island, Massachusetts, USA))

.There are estimated to be over 4000 foraminifera species worldwide. A few are plantonic but most are found on the ocean bottom in the sediment and on surfaces of rocks, corals, shells and other material. Forams have specific habitats with varying requirements for water depth, salinity, and temperature. The species will vary according to location.

Barnacle plates…………(Eggemoggin Reach, Brownville, Maine, USA

Fossil Sand

Caption. (Shark Tooth Ridge, New Mexico, USA)

Caption. (Flagler Beach, Florida, USA)

Caption. (Bois-Gouët, France)

Caption. (Cedar Creek Reservoir, Alabama, USA)

Anthropogenic Sands

Anthropogenic sands are a fourth category, one that is controversial for many collectors. These are sands that are created or modified by human activity. Since they do not occur naturally, they are not true sand. Glass and slag are relatively easy to recognize and certainly are not natural. Native rock that was crushed in mining and dump does look natural after it has weathered for 100 or more year. Plastic in never natural but it does passes through sand-sized are it breaks into smaller pieces.

Glass (Ele‘ele, Kauai, Hawaii, USA)

Stamp sand. (Lake Superior, Houghton, Michigan)

Trinitite. (Alamogordo, New Mexicon)

Brick. (Hudson River, New York, USA)

Plastic. (Mizell-Johnson State Park, Florida, USA)

Slag. (Wells Cree Basin, Tennessee, USA)

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What is Sand?

Sand is formed by the breakdown of pre-existing rocks by weathering and erosion and from material that forms within the depositional environment. The breakdown produces two products: mineral grains and lithic or rock fragments. Grains that form in a depositional environment are typically biogenic in origin, such as the skeletal remains of marine organisms. Some grains are formed by chemical reactions.

Most people think of sand as the granular material at the beach or on a desert. However, to geologists, "sand" is defined as a sediment in the size range of 0.063 to 2 mm. And within that scale, "sand grains" ranges from very coarse (2 mm) to very fine (0.063 mm). On either end of the grains-size scale, the clasts larger than "sand" include boulders cobbles, and pebbles. On the finer than "sand" scale, there is silt and clay.

MINERAL GRAINS IN SANDS

A large number of different minerals may occur in sand. We'll describe the most common.

Quartz

Feldspar

Feldspar is technically a mineral group with varying amounts of calcium, potassium and sodium. With variations in chemistry, the grain color can be clear to cloudy, pinking, orangish, or yellowish.

Mica

Olivine

Heavy Minerals.

Garnets

Garnets range in color from red to pink to orange and are common in sands. Their crystals form dodecahedrons–12-sided crystals; and as they weather, the grains become more and more rounded. Garnets are a group of silicate minerals with varying amounts of iron, magnesium, manganese and calcium in their chemical composition; their color reflects their mineral chemistry. They are often associated with metamorphic rocks. Garnets are common in heavy-mineral sands.

Magnetite and Ilmenite

Magnetite and ilmenite are both opaque iron minerals found in sand. Magnetite is magnetic. Ilmenite is non-magnetic. Both occur as accessory minerals in igneous rocks, and both are common in heavy-mineral sands.

Other Components of Sands

Lithic or rocky fragments

The breakdown of pre-existing fine-to-medium grained igneous, metamorphic and sedimentary rocks can result in sand-sized fragments of both rocks and minerals.

Fragments of igneous rock

Grains of fine-grained igneous rock such as basalt (blue/black) or rhyolite (reddish) are only found close to their source. Beaches around many volcanic islands are black because they are made up of basalt. Other beaches of volcanic origin may have polished obsidian (volcanic glass) grains. Black sands on volcanic coastal regions may also contain fragments of biogenic organisms intermixed with the black sand. Olivine, an accessory mineral is frequently found in "recent" volcanic sands.

Sands with grains of quartz, feldspar and other dark minerals can represent eroded or "decomposed granite." This is typically found close to its point of origin, such as in a mountain stream.

Fragments of metamorphic rocks

Fragments of sedimentary rocks

Other grains in sands:

Glauconite is an iron silicate that forms in shallow marine environments-- within a depositional environment in response to a geo-chemical process. Glauconite grains are amorphous and are patchy green in color.

Gypsum forms in an evaporative environment.

Halite forms in a evaporative environment.

Ooids are spherical bodies of calcium carbonate less than 2mm in diameter. They have an internal structure of concentric layers and form around a nucleus, perhaps a fecal pellet or grain of sand.