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For freshwater aquaria, gravel is the most common substrate. To prevent damage to fish, gravel should not be sharp. Aquarium gravel can be as coarse as pea-sized or as fine as 1–2 mm. [1] It is available in a number of colors, and may be naturally colored or dyed, and may have a polymer seal to ensure it does not affect water chemistry. [1]
The PI is the difference between the liquid and plastic limits (PI = LL-PL). Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 (non-plastic) tend to have little or no silt or clay. Soil descriptions based on PI: [8] (0) – Non-plastic (<7) – Slightly plastic (7-17) – Medium plastic
The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and grain size of a soil. The classification system can be applied to most unconsolidated materials, and is represented by a two-letter symbol. Each letter is described below (with the exception of Pt):
For example, if a soil is 70 percent sand and 10 percent clay then the soil is classified as a sandy loam. The same method can be used starting on any side of the soil triangle. If the texture by feel method was used to determine the soil type, the triangle can also provide a rough estimate on the percentages of sand, silt, and clay in the soil.
The type of clay that is formed is a function of the parent material and the composition of the minerals in solution. [13] Clay minerals continue to be formed as long as the soil exists. [14] Mica-based clays result from a modification of the primary mica mineral in such a way that it behaves and is classed as a clay. [15]
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In a defined sequence, the key asks for the presence or absence of certain diagnostics in a certain depth range. In addition, the key asks for single characteristics, e. g., a certain clay content or a certain base saturation. The soil belongs to the first RSG, for which it fulfils the set of criteria.
Clay is a type of fine-grained natural soil material containing clay minerals [1] (hydrous aluminium phyllosilicates, e.g. kaolinite, Al 2 Si 2 O 5 4). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as a reddish or brownish colour from small amounts of iron oxide .