Rutile exhibits bireflectance and internal reflections in a variety of colors and on twin lamellae rutile shows distinct anisotropy. Rutile appears light gray in reflected light with a reflectance not dissimilar to magnetite although Nb- and Ta-bearing rutile is darker. The strong color, high relief, twinning and extreme birefringence can be used for identification. Violet and orange coloration can be due to Sb or W content or as a result of secondary oxidation. 3B) with the strength of coloration controlled by the Nb, Ta and Fe 3+ content. In thin section rutile is normally reddish-brown ( Fig. Other elements such as Fe, Cr, Ta and Nb, and also tri-valent Ti, can substitute for Ti 4+ with a marked effect on the unit cell dimensions and they are accommodated in the structure by defect structures and crystallographic shear planes. The cell dimensions of pure rutile are a 4.594, c 2.959 Å ( Fig.
In the structure, the titanium atoms lie at the center of a nearly perfect octahedron consisting of six oxygen atoms. It has been reported from lunar rocks and from meteorites where it is commonly Nb-rich, the Nb isotopes having been used to date events during the early stages of formation of the solar system. In igneous rocks it occurs both as dispersed very small grains and as large crystals in pegmatites and it is also found as a detrital mineral in sediments. It occurs in metamorphic rocks such as amphibolites, eclogites and kimberlite xenoliths. Rutile (TiO 2) has a tetragonal structure (space group P4 2/ mnm.). It has low reflectance in reflected light and the high hardness can cause difficulties during polishing that leave many surface scratches that are nevertheless an aid to identification.
Corundum has a high hardness (9 on Mohs scale). There is often some zonation and alteration lamellae may be present. In thin section corundum has a high relief and it is generally colorless although tinges of the red of ruby or the blue of sapphire can sometimes be apparent. These unstable phases are β-Al 2O 3 (hexagonal), γ-Al 2O 3 (cubic), δ-Al 2O 3 (tetragonal or orthorhombic), κ-Al 2O 3 (orthorhombic or hexagonal), ε-Al 2O 3 (hexagonal), η-Al 2O 3 (cubic) and σ-Al 2O 3 (cubic). In addition to corundum (α-Al 2O 3) there are natural and synthetic Al 2O 3 phases that are not considered as polymorphs but are transitional stages between corundum and the Al-hydroxides. The effect of these impurities is to color the corundum, causing the red of ruby, the blue of sapphire and green, yellow, orange, pink, and brown varieties ( Fig. Most of these elements are usually only present in amounts up to a few hundred ppm but Cr can reach 2–3 wt% and Fe up to 1 wt%. Ĭorundum consists of nearly pure Al 2O 3 with trace to minor amounts of Cr, V, Fe, Ni, Ga, Ca and Mn whilst Na, Mg, Si, Co, Cd, Ga, S and Zr can also occur. Weldon, owned by J Ambalu, Amba Gem Corp, reproduced with permission from Hughes RW, Manorotkul W, and Hughes EB (2017) Ruby & Sapphire: A Gemologist's Guide.
#How to add an atom in crystalmaker software
Oxford, England: CrystalMaker Software Ltd, (C) Reproduced with permission from Bowles JFW, Howie RA, Vaughan DJ, and Zussman J (2011) The Rock Forming Minerals, vol.
#How to add an atom in crystalmaker for mac
Crystal Structure Images Generated Using CrystalMaker®: A Crystal and Molecular Structures Program for Mac and Windows. (C) the color of corundum is determined by the proportions of the trace elements. (A) The unit cell of corundum viewed down the z axis, (B) the unit cell viewed down the x axis.
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