Stone, minerals and semiprecious of the world stone
Oxide and hydrooxide: Evksenite -->rus
Y (Nb, Ti, Ta)2 (O, OH)6
Crystal structure rhombic
Hardness on the Mohs scale 5,5-6,5
Specific unit weight mass 4,3-5,9
Fracture, break padman
Colors black or light-brown
Colors in powder triturate brown-yellow, gold, brown-grey
Glance (glitter, glare) metallic
Good crystals (plate tablet lamellar or short-prismatic) - rare. Colors black, brown-black, velvety-black, rarer greenish-black; often covered the brown crusts of products of change and weathering. Dense the masses are more widespread with typical off-gloss on-the-spot fracture. This mineral is strongly radio-active from the presence of uranium and thorium. To him not place in private collections !!
Composition varies widely, in general answering the formula of Av2o6, A = Y, Yh, Dy, U, Sa, This, Th, Rb, (Fe2+?); In = Nb, Ti, That, possibly, Fe3+, Sn; About substituted for part HIM. A table of contents of Ti is 42-66% from the sum of Ti + Nb + That, 70% exceeds rarely (polycrase is enriched titan). Usually there are a few percents of Ta2O5; maintenance is substantial That only in tantevksenite and, especially, in tantalum- polycrase.
In a group "A" a leading role is played by the elements of rare earths (18,5-35,5% TR2O3); the elements of yttric group prevail sharply among them, while the elements of ceric group are contained in a two-bit, role them a few increases in the varieties enriched a tantalum. The table of contents of uranium mainly hesitates within the limits of 4-8% UO2, rarely arriving at 14-16%; the amount of ThO2 varies from tracks to 6,5%. Besides Sa, Mg and Mn Rb is specified quite often; the presence of Fe is characteristic, presumably, in a kind both Fe2+ and Fe3+. Different maintenance of U was marked different correlation of isotopes of Rb in separate parts of the same crystal, that matters for determination on Evksenite of absolute age. The admixtures of Sc, Zr, Hf, Ge, N, are specified, also century
Usually partly or fully metamict (of or denoting the amorphous state of a substance that has lost its crystalline structure as a result of the radioactivity of uranium or thorium within it) and roentgeno-amorphous. Nometamict Evksenite is exceptionally rare in nature. Crystals columnar, basaltiform, a few extended on an ax with, thick- or thin-plate tablet lamellar on b (010). Crystals are imperfect, measurings of crystals in all of cases are only approximate. Verges are always mat; on the verges of vertical belt the longitudinal shading is developed, on other verges, shading, parallel a rib with b(010) is also ordinary. Twins to on (201) widespread, the featherlike shading is characteristic on the general verge of b (010). Twins are known also to on (101) and to on (111). Chasty subparallel and fan-shaped joint, junction of crystals. Spaynosti is not observed. In thin fragments transparents a yellow-red or reddish-brown color. Strongly radio-active. Does not luminesce in ultraviolet rays. Inductivity 3,74-5,29, most often 4,02-4,63.
Evksenite comparatively easily to distinguish from other minerals on an external type and chemical composition. But easily to entangle him with other difficult oxides, having near composition. Simple chemical tests serve as an indicator on niobium, and also (at the visual study of standard) association with ilmenite. At heating cracking and, as all of metamict minerals, shines. Not melt fuse. In closed tube usually selects a little bit of water.
Origin provenance genesis.
Evksenite - typical mineral of some pegmatites in which he at times be found in a noticeable amount, in an association, foremost with ilmenite, mica and other minerals of rare earths. Continuous the masses of wrong form, crystals, grains.
Deposit minefield mine field occurrence subsoil.
The most known deposit of this mineral is in Sonth Norway. In addition, it is known on Madagascar (where found out wonderful crystals) and in Brazil.