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▪ I. spinel|ˈspɪnəl|
Forms: 6 spynel, 7 spinnell, 7–9 spinell, 8–9 spinal, 7– spinel.
[ad. older F. espinelle (mod.F. spinelle, It. spinella, Sp. espinela). See also espinel and spinelle.]
1. a. A gem or precious stone of a red or scarlet colour, closely resembling the true ruby, now classed as belonging to the typical species of the spinel group of minerals (see sense 2).
1528MS. List of Jewelry (P.R.O.), xiij rynges,..iij with Spynels,..oon with a crapawd. 1599Hakluyt Voy. II. 236 Rubies, Safires & Spinels. 1620in Rymer Foedera (1710) XVII. 196 Two greate Stones called Spinnells. 1665Sir T. Herbert Trav. (1677) 88 Translucent stones which want neither beauty nor esteem; namely, Topazes, Amethysts, Spinels [etc.]. 1698Fryer Acc. E. India & P. 214 The third sort of Ruby is called a Spinell. 1801T. Thomson in Encycl. Brit. Suppl. II. 203/2 If deep [red], the ruby is usually called balass; if pale rosy, spinell. 1892Daily News 23 Mar. 5/4 The Spinel and the Balas, the one a lively poppy-red, the other a violet-rose, frequently usurp the dignity of a true ruby.
b. More fully in spinel ruby.
1668Charleton Onomast. 277 Rubinus Spinellus, the Spinel Ruby. 1753Chambers' Cycl. Suppl. s.v. Ruby, The second is the spinal ruby. Under this name they [jewellers] know those rubies, which are of a somewhat less deep..colour, than what they call the true ruby. 1796Kirwan Elem. Min. (ed. 2) I. 253 Spinell and Balass Rubies. 1815J. Smith Panorama Sci. & Art II. 411 In the emerald it [chromium] exists in the state of green oxide, and the spinal ruby contains it in the state of an acid. 1839Ure Dict. Arts 391 If..we make the edges of a spinel ruby..curvilinear. 1883Encycl. Brit. XVI. 386/2 Varieties are—Spinel ruby when scarlet, Balas Ruby when rose-red.
2. Min. The typical species of a group of minerals (the spinel group), which are compounds of sesquioxides with protoxides, and crystallize in the isometric system. The formula of the typical species is MgAl2O4.
1807T. Thomson Chem. (ed. 3) II. 482 This mineral, which has some resemblance to the spinel, was found composed of 60 parts alumina [etc.]. 1817R. Jameson Char. Min. (ed. 3) 132 Triple crystals occur in spinel and calcareous-spar. 1842Penny Cycl. XXII. 348/2 Spinell is found in Ceylon and Siam in isolated and rolled crystals in the beds of rivers. 1888Rutley Rock-Forming Min. 108 Ordinary spinel appears reddish, or colourless by transmitted light. 1953F. H. Pough Field Guide Rocks & Minerals ii. 141 Spinel, like corundum, is a mineral of metamorphosed limestones and low-silica pegmatites, and consequently it is commonly associated with corundum. 1977A. Hallam Planet Earth 137 The name spinel broadly refers to a group which includes the minerals magnetite and chromite. In a narrower sense, spinel is the magnesium aluminum oxide member of the group.
b. One or other of the various minerals belonging to this group. The general formula of the minerals is A2+B23+O4, spec. where B is Al. The name is also applied to any of a large number of artificial minerals having similar structures.
See also chloro-spinel (chloro-1) and water-spinel.
1837Dana Min. 328 The fine colored spinels, when of large size, are highly esteemed as gems. 1863― Man. Geol. 139 The soft spinels of St. Lawrence co., called houghite. 1880E. Cleminshaw Wurtz' Atom. The. 144 The spinels form a very natural isomorphous group. 1944C. Palache et al. Dana's Syst. Min. (ed. 7) I. 688 In addition to the natural spinels a considerable number of artificial spinels have been described, where A = Co, Cd, Cu and B = Co, Ti, Sn, V, Ga, In, Mn. One of the further complexities of composition in the artificial spinels is a tendency for substitution of A atoms for part of the B atoms of the formula, i.e., the formula may be written BABX4 (as in the compounds GaMgGaO4, etc.). 1967D. H. Martin Magnetism in Solids i. 39 The two crystal types to which the most fully investigated ferrimagnetics belong are those known as ‘spinels’ and ‘garnets’. 1974D. M. Adams Inorg. Solids iii. 69 The structure of a spinel is conveniently described by a parameter γ which equals the fraction of A2+ in octahedral sites. Thus, for a ‘normal’ spinel, γ = 0, for an ‘inverse’ spinel, γ = 1. A random distribution of A2+ amongst the two groups of sites gives γ = 2/3.
c. attrib., as spinel-crystal, spinel structure.
1851Amer. Jrnl. Sci. Ser. ii. XII. 210 Some of his specimens are spinel crystals..in one part, and true Houghite in another. 1944C. Palache et al. Dana's Syst. Min. (ed. 7) I. 688 Another chemical feature of interest is the ability of artificial Mg, Al spinel to contain considerable excess of Al2O3 without impairment of the spinel structure. 1967M. Chandler Ceramics in Mod. World vi. 178 Today most ferrites have spinel structures.
▪ II. spinel
var. spinal n.; obs. or dial. f. spindle. |