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III. -- The Basalt of the Moabite Stone

By Professor T. G. Bonney, D.Sc., LL.D., F.R.S.

The Geological Magazine, New Series.
DECADE IV. VOL. IX. January - December, pp. 493-495 (1902)

Installed as a webpage on Shade Tree Physics on 16 Dec 2010.

493

    A block of basalt, bearing an ancient inscription in a Semitic language, was discovered in 1868 at Dhiban (the Dibon of Scripture) by the Rev. F. A. Klein, of the Jerusalem Mission Society. This block, which measured 3' 10" x 2' 0" x 1' 2.5", proved on examination to have been erected by Mesha, King of Moab about 890 B.C., and to refer to the war mentioned in 2 Kings iii. A series of blunders on the part of those anxious to obtain this interesting relic caused a quarrel about ownership between two Arab tribes, and one of them, to spite the other, broke it in pieces. These, however, were obtained by the French Consul in Palestine, and sent to Paris, where they were fitted together so far as possible, and the



494     Professor T. G. Bonney--Basalt of the Moabite Stone

repaired stone is now in the Louvre Museum.1 The late Professor E. H. Palmer, on a visit to Dhiban in 1870, picked up a small fragment from those still lying on the spot, which he gave to me on his return to England. The constant pressure of other work has hitherto prevented me from examining the specimen, and I have only recently had a slice prepared. The largest face of the fragment measures about 3" x 2.5", but the thickest part hardly exceeds half an inch. The original smoothed surface of the stone, possibly including part of a letter, may be seen on one of the sloping sides.
    The rock apparently is in good preservation; minutely granular, nearly black in colour, but proving on a closer examination to be speckled with more than one dark mineral, and with less definite greyish spots, all very small. Its specific gravity (by a Walker's balance) is 2.89. The slice, when examined under the microscope, exhibits a porphyritic structure, though on a small scale, no one of the minerals exceeding about .05" in diameter. They are:--(a) Augite, not abundant, brown in colour, the grains presenting a rather corroded aspect both externally and even internally, partially including, in one instance, a small grain of the next mineral. (b) Olivine, rather abundant, rounded or slightly irregular in outline, occasionally showing a fairly well-developed brachypinacoidal and an imperfect macropinacoidal cleavage. A brown staining has affected the exterior of most grains, and penetrated for a short distance into cracks. This, in addition to a very faint yellowish tinge in the grains, shows the olivine to be a rather ferriferous variety. (c) Iron-oxide, hematite, or perhaps ilmenite, with a rusty-looking exterior; (d) felspar: this, like the last-named mineral, varies so much in size that it is difficult to draw the line between crystals occurring porphyritically and those in the base. In no case do the extinction angles give very decisive evidence, but they suggest that labradorite is at any rate the dominant species.
    The minutely holocrystalline groundmass, except for one or two small patches, consists of lath-like plagioclases, up to about .004" in length; of stumpy, not very well-formed prisms of brown augite, about .002", and of granules of iron-oxide. The patches, small2 and not numerous, are formed by a fairly clear mineral, which, however, includes some very minute films, giving bright polarization tints, its own being very low, not rising above a greyish or slightly pinkish white. Each patch generally consists of two or three grains, and is without a definite external form. The small felspars and augites are sometimes included by or project into these patches from the surrounding matrix, which has no regular boundary. The mineral resembles a lime carbonate (there is no distinct cleavage), and I observed, on applying some hydrochloric acid to the cut surface, a rather brisk effervescence at a number of points; hence, I conclude it must be calcite, probably not very pure. But though it occurs

    1   Palmer: "Desert of the Exodus," pt. 2, ch x. For the inscription see Ginsberg, "Moabite Stone." A figure and succinct account are given in Chambers' Encyclopaedia, s.v. Moabite Stone.
    2 The diameter of the largest is about .03".

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sporadically it does not seem to fill a cavity, or to have replaced a less stable species of felspar, which indeed, as the rock is in good preservation, is hardly probable. So I think the mineral must have been present as a constituent when the rock was molten, and can only suppose that the latter, on its ascent to the surface, caught up some intervening limestone, and the pressure sufficed, as in a case of contact metamorphism, to prevent the dissociation of the carbonate, which here and there retained its identity in the viscid mass.1 This occurrence in such a rock as basalt, is, I think, rather unusual.

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    1 For cases of the imperfect digestion of a carbonate in an igneous mass, see J. Parkinson, Q.J.G.S., lvii (1901), p. 198, and A.K. Coomáraswámy, id., lviii (1902), p.399.



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