Special Features : Gibbsite

A mineral found in highly weathered soils such as Ultisols and Oxisols, and in special condition, in the Inceptisols and Andisols.

Aluminum oxyhydrate crystallizes when soil pH is greater than 5.5 and the most common mineral is gibbsite. Boehmite, the mono-hydrate is rare.

Special Features : Goethite

Iron crystallizes in soils as different minerals, goethite and hematite, and each with different shapes or habits.

Special Features : Halite

Present in salt affected soils. Cannot be seen in thin sections as it is isotropic. The most common habit is the cube or pseudo-cube. A fibrous form may be picked from soil surfaces (puffed solonchaks). Malformations such as the "hopper structure" may be encountered.

Special Features : Pyrite

Forms in recent marine sediments. Present in Entisols and Inceptisols developed on these sediments. Bacterial decomposition of organic matter releases sulfur which combines with sulfate to form the pyrite. When soils with pyrite are drained, the mineral oxidizes to release sulfuric acid. The strong acidity makes the soils unproductive.

Special Features : Gypsum

A common mineral in Aridisols.

Special Features : Whewellite

A calcium mineral that crystallizes in cells of plants (also one of the minerals that cause kidney-stones). The fine crystals can choke the plant and pack closely in a plant cell.

Special Features : Common Minerals

Quartz is present in all soils. Well formed crystals showing the typical trigonal symmetry under the microscope is rare and when seen, is inherited from the original rock.

Allophane is a complex alumino-silicate and has a short-range order or is poorly crystalline. It has a large surface area and when present in Andisols, imparts some special properties to the soil.

Special Features : Manganese Minerals

A number of manganese minerals may be present in soils depending on the conditions. Manganite is common in most well drained soils. In some soils developed on basalts, nsutite and lithiophorite may occur.

Special Features : Sulfate Minerals

Apart from gypsum, many other sulfate minerals can occur in soils. Celestite is rare and barite is very insoluble. Both have been reported in Aridisols.

Special Features : Diatoms

Diatoms are organisms that live in sediments. Their skeleton is made of silica. There are hundreds of different kinds of diatoms. Some sediments are called diatomaceous earths, as their entire structure is composed of these skeletons. Inhaling dust composed of Diatoms can cause lung damage.

Special Features : Unique Minerals

Collophane is a crypto-crystalline phosphate mineral. Rare in soils and generally found in soils influenced by phosphatic deposits.

Soils rich in carbonates may have siderite present. This mineral is blood red under the microscope. Rare, but may be found in calcareous wet soils.


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