Sandstone

a SEDIMENTARY ROCK made up of sand grains with sizes between 0.06 mm and 1 mm, and a variety of other minerals and materials cementing the grains together. CALCITE is a common cement, and silica (as QUARTZ) cements sands to produce a hard sandstone often referred to as an orthoquartzite (to tell it apart from the metamorphic rock, quartzite). Brown and red sandstones usually have an iron-rich cement such as LIMONITE or haematite. Other minerals which may be present include FELDSPAR and MICA.

Taken from Dictionary of Science

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Sandstone (sometimes known as arenite) is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.

Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material. However, some that have been used in the past, such as the Collyhurst sandstone used in North West England, have been found less resistant, necessitating repair and replacement in older buildings. Because of the hardness of the individual grains, uniformity of grain size and friability of their structure, some types of sandstone are excellent materials from which to make grindstones, for sharpening blades and other implements. Non-friable sandstone can be used to make grindstones for grinding grain, e.g., gritstone.

Rock formations that are primarily composed of sandstone usually allow percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.

Taken from Wikipedia

Karyotype

the number, shapes and sizes of the chromosomes within the cells of an organism. Every organism has a karyotype that is characteristic of its own species, but different species have very different karyotypes. For example, all normal human females have 22 pairs of DIPLOID chromosomes with a similar shape and size, but all female horses have 32 pairs of diploid chromosomes which have their own unique shape and size.

Taken from Dictionary of Science

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A karyotype is the characteristic chromosome complement of a eukaryote species. The term may also be used of a cell, or an individual. The preparation and study of karyotypes is part of cytogenetics.

The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. Thus, in humans 2n = 46. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23).

So, in normal diploid organisms, autosomal chromosomes are present in two copies. There may, or may not, be sex chromosomes. Polyploid cells have multiple copies of chromosomes and haploid cells have single copies. The study of whole sets of chromosomes is sometimes known as karyology. The chromosomes are depicted (by rearranging a microphotograph) in a standard format known as a karyogram or idiogram: in pairs, ordered by size and position of centromere for chromosomes of the same size.

Karyotypes can be used for many purposes; such as, to study chromosomal aberrations, cellular function, taxonomic relationships, and to gather information about past evolutionary events.

Taken from Wikipedia