Explore the unique properties of diamond and graphite, two crystalline forms of carbon, and how their crystallization is influenced by cooling rates. Discover the differences in their macroscopic properties and how they are used in various applications.
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[...] Basalt forms, above oceanic ridges, by crystallization, during the ascent of magma. Gabbro forms, on the other hand, by crystallization in the magma chamber, under the same ridge. Basalt forms under conditions of lower pressure and temperature than that of gabbro. Based on the hypotheses that the cooling of a magma allows the formation of crystals and that the cooling rate produces crystals of different sizes, we can use the crystallization experiment of vanillin. Vanillin is deposited on a microscope slide that is heated to 82°C, the melting temperature. [...]
[...] This weak interplanar interaction makes graphite a fragile material and a poor conductor. Activity 2 - Crystals in Rocks The observation of thin sections shows that these 2 rocks have the same minerals (Olivine, pyroxene and plagioclase) but there is an important difference in the structure of the two rocks. The basalt appears to be composed of minerals of varying sizes embedded in a dark, non-mineralized 'paste', a glass. The basalt contains microlites and the minerals are disordered, so it is an amorphous solid. [...]
[...] Diamond and graphite are two crystalline forms of the same entity, carbon. This first observation is made possible by the phase diagram which allows two distinct solid states (diamond and graphite) to be matched to a condensed state of matter obtained by the solidification of a liquid. These two crystalline solids are regular periodic assemblies of carbon atoms. The smallest structure of this assembly forms a unit cell. The position of the carbons in this unit cell allows to distinguish the two types of crystal networks. [...]
[...] In the case of slow cooling, the crystals formed are of large size, type phenocrysts. On the other hand, rapid cooling gives rise to small crystals, type microlites, accompanied by a glass. Since basalts and gabbros differ only by the size of their crystals, we deduce that their origin is common, and that they are respectively derived from a rapid and slow crystallization of a basaltic magma. The examples of limestone and granite (docs 2 and show that a rock is composed of the association of a single type of minerals (calcite crystals for Carrara marble) or different minerals (Plagioclase, biotite, quartz, and orthose for granite). [...]
[...] The minerals differ by their chemical composition and crystal structure, which gives them a different appearance at the microscopic (polarization colors, relief . ) and macroscopic (color, luster . ) scales. They have a scale of the order of a few millimeters to a few centimeters. The elementary mesh, the smallest repetitive structure of a crystal, has a scale of the order of the nanometer. The crystal, on the other hand, has a very variable scale usually below the millimeter. Some phenocrysts can measure up to several centimeters. [...]
