13 Mayıs 2013 Pazartesi

American Samoa Territorial Mineral

American Samoa Territorial Mineral

Calcareous Sand

Sand is a loose, granular material made of disintegrated rocks and minerals. It is mainly composed of silica-based rocks and, in tropical regions, calcium carbonate. Sand primarily made of calcium carbonate is called calcareous sand and is composed of debris from once-living marine organisms. These plants and animals used calcium carbonate to form their skeletons and shells. When the organisms died, these pieces became part of the beach sand.
The National Park of American Samoa has miles of pristine and scenic coastline, particularly its stretch of white sand beach rimmed with coconut palms. Like many other geologically young islands, American Samoa is not rich in mineral deposits. Crushed sand, however, is mined, and American Samoa’s well-known sand makes a suitable representative of the territory’s geology, economy, and natural resources.
When pieces of coral and mollusks break off in the seas, either by human intervention or natural disturbances, they eventually form part of beach sand. When green algae leaves die, those also become part of beach sand. Echinoderm skeletons and foraminifera shells do the same when those organisms die. All of these elements are made of calcium carbonate and compose calcareous sand. Calcium carbonate is the same material that forms limestone and human skeletons.
Calcareous sand by definition contains one to as much as 100 percent calcium carbonate by weight. These organic calcium carbonate particles can settle on a nearby beach or travel thousands of miles. The distance traveled plays a large part in the erosion, size, and rounding of the particles. The remainder of the sand is composed of the element silica. Silica is the primary component of beach sand in temperate regions, while calcium carbonate is a component of sand mainly in tropical regions.
Because the availability of calcium carbonate increases with water temperature, calcareous sands occur on many tropical islands.
Sand is in constant demand for use in construction of buildings and highways. Because of its density, sand is relatively costly to transport, so local sources are sought when possible. Calcareous sands are used in the construction of golf putting greens. However, there are suspected problems with drainage and long-term stability of these sands due to potential breakdown of the calcium carbonate.
State Mineral
Sand Beach in American Samoa
State Mineral
Close-up of Calcareous Sands
State Mineral
Composition of Calcareous Sand (waynesword.palomar.edu)
State Mineral
Wave Action on the Sand
CALCAREOUS SAND FACTS (properties listed are for the calcium carbonate component)
Group: Carbonate mineral
Chemical Formula: CaCO3
Crystal Structure: Trigonal hexagonal
Hardness (Mohs): 3
Color: Colorless or white, also gray, yellow, green
Transparency: Transparent, Translucent
Luster: Vitreous, Pearly
Density: 2.7102(2) g/cm3
Streak: White
Cleavage: Perfect
Perfect on {1011}.
Fracture: Irregular/Uneven, Step-Like
Tenacity: Brittle

Some data courtesy of the Mineralogical Society of America
Author: World Trade Press

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