Apatite hardness

Intermediate Hardness (4) Fluorite, soft phosphate, magnesite, limestone (5) apatite, hard phosphate, hard limestone, chromite, bauxite (6) feldspar, ilmenite, orthoclase, hornblendes. 

The hardness of a mineral as measured by the Mohs scale is a criterion of its resistance to crushing [Fahrenwald, Trans. Am. In.st. Min. Metall. Pet. Eng., 112, 88 (1934)]. It is a fairly good indication of the abrasive character of the mineral, a factor that determines the wear on the grinding media. Arranged in increasing order or hardness, the Mohs scale is as fohows 1, talc 2, gypsum 3, calcite 4, fluoride 5, apatite 6, feldspar 7, quartz 8, topaz 9, corundum and 10, diamond. 

Nanostructured materials are nothing new. Chrysotile fibers are an example (Fig. 16.22), as are bones, teeth and shells. The latter are composite materials made up of proteins and embedded hard, nanocrystalline, inorganic substances like apatite. Just as with the imitated artificial composite materials, the mechanical strength is accomplished by the combination of the components. 

Major structural components of hard parts Ca, C, SI, 0, P, F, Sr, S Calcite, aragonite, opaline silica, celestite, apatite, fluoroapatite Components of frustules and tests, bone, teeth... 

Cement, dentin, and enamel are bone-like substances. The high proportion of inorganic matter they contain (about 97% in the dental enamel) gives them their characteristic hardness. The organic components of cement, dentin, and enamel mainly consist of collagens and proteoglycans their most important mineral component is apatite, as in bone (see above). 

Thus, although this structure cannot be described or understood in terms of any regular anion array or any connected array of cation-centred polyhedra, it is readily and logically visualised as an alloy framework with anions inserted into appropriate (usually tetrahedral) interstices. It must be pointed out, however, that there is a very small distortion of the MusSia structure to give the cation anay in apatite. This consists of a slight rotation of each of the colunms ( rosettes ) at [OOz] - in Fig. 37 clockwise by about 4 . This affects the symmetry, but hardly the geometry. 

Although about 80—90 percent of the total citric acid in humans are localized in hard tissues as enamel, dentine, cementum and bones, very little is known on the biological function of citric acid in biocalcification. HA crystals are reported to be dissolved by the action of citric acid. The acid dissolves the crystals in such a way that the destruction is a preferential attack along the c-axis. It is highly probable that the HA crystallites present in mineralized tissues also do have a dislocation in the centre of the material 165). Another assumption describes that citric acid is a constituent of the aqueous phase of enamel or that citrate is bound to the surface of apatite by adsorption166). 

Hohling, H. J., Themann, H., Vahl, J. Collagen and apatite in hard tissues and pathological formations from a crystal chemical point of view. Calc. Tiss. Proc. 13rd. Europ. Symp. on Calc. Tiss., p. 146. Berlin, Heidelberg, New York Springer 1966... 

Hohling, H. J., Schopfer, H. Morphological investigations of apatite nucleation in hard tissues and salvary stone. Naturwissenschaften 55, 545 (1968)... 

Apatite [1306-05-4] -flotation recovery of [FLOTATION] (Vol 11) -hardness of [ABRASIVES] (Vol 1) -lanthanides from [LANTHANIDES] (Vol 14)... 

Reconstituted acid-soluble collagen from various mineralized and unmineralized tissues have been examined for their potential to pick up calcium and phosphate from buffered solutions, and for their capacity to induce nucleation of a mineral phase426-434. Some collagens were good, others poor catalysts428,429 and apatite deposition proceeded in the presence of soft as well as of hard tissue collagens. The uptake of calcium ions requires the presence of phosphate ions and vice versa the Ca/P ratio is close to that of apatite (1.5—1.8)431. Study of exchange reactions by isotope tracers between solvent und substrate revealed that in absence of either... 

In invertebrates, collagen is uncalcified, whereas in vertebrates it occurs in the form of soft and hard tissue. Remains of the earliest vertebrates — bony armour — are found in sediments of the Ordovician (ca. 500 million years). At about that time, conodonts appeared in the stratigraphic column mineralogically they are carbonate apatite. Conodonts are small tooth-shaped fossils 0.2 to 3 mm in size whose origin is in doubt they are most likely remains of some unknown chordata that became extinct in Triassic time516. ... 

Newesely, H. Conditions for the existence of octacalcium phosphate, withlockit and carbonate apatite. A contribution to the crystal chemistry of biological hard substances. Dtsch. zahnarztl. Ztschr. 20, 754-766 (1965). 

Despite its tremendous strength, glass can be fairly easy to abrade. On the Mohs scale of hardness,f glass is between 5 (apatite) and 7 (quartz). So, glass can scratch materials with lower numbers (for example, copper, aluminum, and talc). Likewise, glass can be scratched by materials that have higher numbers (for example, sand, hard steel, and diamond). 

Poorly crystalline or amorphous Phosphorite sediments made from the hard remains of marine organisms are the principal commercial source of phosphates, although Apatites are also mined. Treatment of phosphate minerals with sulfuric acid yields superphosphate fertilizer, a mixture of Ca(H2P04)2, H3PO4 and CaS04. Phosphoric acid treatment gives triple superphosphate , rich in Ca(H2P04)2. Other soluble fertilizers such as ammonium phosphates are obtained from these products. 

Phosphates are found in soft organic tissues as phosphate esters, and in hard tissues, notably bones and teeth, as solid calcium orthophosphates see Biomineralization). Hard tissues are composites of Apatite and an organic matrix collagen in bone, dentin, and dental cement, and keratin in dental enamel. The Apatite phases are defective with Ca/P ratios of 1.6-1.8 and can incorporate other cations (Na+, K+, Mg +) or anions (F , d , COs ", citrate). 

In 1812, German geologist Frierich Mohs (1773-1839) devised a scale with specimen minerals that offered comparison of hardness qualities that allows the assignment of a Mohs hardness number to a mineral. Mohs scale utilizes ten specific representative materials that are arranged numerically from the softest (1) to the hardest (10). The reference minerals are (1) talc, (2) gypsum, (3) calcite, (4) fluorite, (5) apatite, (6) orthoclase feldspar, (7) quartz, (8) topaz, (9) corundum, and (10) diamond. 

---