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.
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,
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
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".
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.
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.