Good medium density, crispy, creamy, has a flavor “after the rain”. Delicious chalk.
Origin of chalk
Cretaceous period of time is called, covers approximately 80 million. Years during the reign of the dinosaurs. Warm and small (30-500 meters deep) sea that time gave shelter to the myriads of tiny mollusks build their skeletons and shells from calcium produced from water.
The remains of these creatures, accumulated in the bottom sediments of many-layers, and become a good friend of us chalk. As a percentage of the mineral chalk is divided into the following parts:
- fragments of skeletons – about 10%. It is not just about the simplest beings, but also of multicellular animals, endowed with the ability to extract and the concentration of calcium in the tissues.
- microscopic shells of mollusks foraminifera – about 10%. However, not all rhizopod (Russian name of the animals) were calcareous shell. Some constructed of a protective layer hitinopodobnogo substance. In many respects, therefore, the actual Cretaceous calcium carbonate is searched no more than 98% (not less than 91%).
- fragments of calcareous algae – up to 40%. Coccolithophorids – plant plankton of the oceans – and feels great in our time. Up to 98% suspension of microscopic live in the upper layers of the seas and had to account for this type of algae. Therefore calcareous mineral, actually – for the most part a product of vegetable and non-animal origin. Origin of Cretaceous – merit of plants!
- fine crystalline calcite – 50%. We are talking about the “wreckage debris”, and so a miniature size, which determine their biological affiliation is not possible.
- insoluble minerals (silicates mainly) – up to 3%. Basically it is a geological debris (sand and fragments of various rocks), listed in the Cretaceous sediments by winds and currents. Although the addition of calcium biogenic formation enriched silicon and phosphorus compounds during the metabolic processes in the animal’s life.
Shells more or less large mollusks, coelenterates skeletons, alien mineral concretions in the Cretaceous strata are relatively rare. Only some chalk photo exhibit observer arrays spotted with voids volume of shells.
The composition of chalk
Conventionally, it is believed that the chemical formula corresponds to the formula chalk calcium carbonate CaCO3. However, the actual composition of the chalk differs from the composition of the calcium salt of carbonic acid.
Actually calcium oxide in about half of the mineral: CaO concentration ranges from 47% to 55%. Many in the Cretaceous and the carbon dioxide that is in a bound state. CO2 – 43%!
MgO Magnesium oxide may be up to 2% by weight of chalk. SiO2 quartz inclusions are usually not very significant, but in general are required, and can be up to 6% concentration. The density of the chalk with a high silicon content than usual.
Several less composed of alumina Al2O3 chalk – less than 4%. A variety of iron oxides rarely exceed half-point threshold concentration, but they are painted in red chalk quite often.
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