A NOTE ON ITACOLUMYTE, OR FLEXIBLE

SANDSTONE.

BY ALFRED MORGAN.

IN investigating the mineralogy of the precious crystals, the "flowers of the mineral kingdom," my interest in that variety of elastic sandstone to which the somewhat fanciful name of Itacolumyte has been given, was awakened. And I have lately found, in the Records of the Geological Survey of India,* a paper by Mr. H. B. Medlicott, A.M., F.G.S., containing fuller information on the nature of this remarkable rock than I had hitherto met with.

It is a prevalent notion that in the Itacolumyte of Brazil we have the true matrix of the diamond. This assertion, which is without proof, has been repeated in many works on gems and precious stones. No authentic instance has yet been produced of its diamondiferous nature, and in India there is not a shadow of such a connexion existing. According to Dana, the Itacolumyte of Brazil, which is associated with gold and topaz, is a micaceous granular quartz rock, which breaks into slabs like gneiss, or mica slate.

In India, the name Itacolumyte has been given to a local and modified condition of a massive quartzite, or metamorphic sandstone. It contains but few and isolated plates of mica, and is devoid of any schistose (foliated) structure. The only known habitat in India of the elastic sandstone is Kaliana, five miles west from Dadri, a small town in the Jheend State, and sixty miles west of Delhi. The hill systems in the neighbourhood are regarded as prolonga

* Vol. vii., p. 31. 1874.

tions of the Aravali region of disturbance. The highest part of the ridge that overhangs the village of Kaliana, is double crested, the projecting rocks being two strong beds of ironstone, a quartzite strongly impregnated by massive specular iron (black hæmatite), and some strings of pure ore, occurring locally with magnetic iron. Colonel McMahon, who communicates the particulars, says, further, that "the ferruginous quartzite is regularly interstratified with mica and hornblende schists, and that an earthy cellular quartzite also occurs, largely used for millstones. All the series are nearly vertical. The elastic sandstone is only found in patches in this band of millstone quartzite. There is no regular bed or seam of it; the stonecutters, of whom there is quite a colony at Kaliana, come upon it suddenly when cutting out slabs of the ordinary stone. Often the rock in immediate contact with a nest of the elastic sandstone is highly indurated and quartzose. The stone-cutters declare they sometimes find it in the line of the bedding, and sometimes in the joints. Their idea of the matter is, that it is a mere local peculiarity of the sandstone rock, caused by the percolation of rain water and miti (earth) from the surface."

It is probable, as Mr. Medlicott observes, that if the miti had been omitted, the natives' explanation is the correct one. Superficially examined, the only difference observable is the greater porosity and friability of the elastic stone, as compared with the ordinary quartzite; and the peculiarity of flexibility is probably due to the mechanical removal by water of some thinly permeating cement, to which the strong rigidity of the quartzite is due. The beautiful specimen of the Delhi stone that I exhibit this evening, was presented to the Liverpool Free Public Museum by Mr. Robert Gladstone. It measures 18 inches in length, 8 inches in width, and of an inch in thickness, and the amount of the deflec

tion from the plane that it indicates, when supported at each end, is equal to 1 inches. There is also a fine specimen of the Brazilian variety in the Free Public Museum. With respect to the quality of flexibility-the stone bends very readily up to a certain point, and then comes to an abrupt stop. Mr. F. R. Mallet* found that a slab of the Kaliana stone, measuring 24.5" x 6.7" x 1.8", resting upon supports 24" apart, gave a deflection of 0.7", and that, after saturation with water, this amount of deflection was very considerably reduced.

The Brazilian variety has a mottled, greyish appearance, and is of a finer grain than the Kaliana specimen. Its length is 13", width 91", and thickness". I am indebted to the Committee for kindly lending me the specimens for examination. Professor Haughton thus explains the property of flexibility +-"A most remarkable circumstance sometimes occurs in the formation of these sandstones, which are not composed of pure particles of quartz, but of clay mixed with them, namely, that the particles of quartz mixed in this clay or paste are permitted a certain amount of motion. If you take an ordinary sandstone, it is like any other rock, and with a lens you can see the separate particles, and that each separate particle is touched on every side by a number of other rounded particles that hold it in its place, and it in turn contributes to hold them in their places, so as to form of the whole a rigid rock, like any other. But, occasionally, in some rare cases-which, as far as I have any knowledge of them, are confined to Brazil, South Carolina, and Delhi-you have a rock composed of particles of sandstones, which are not in contact with each other, but lie in a paste of felspathic clay, which clay permits a certain amount of motion between the particles of the mass."

* Op. Cit.

+ Manual of Geology. Haughton. Lecture ii., p. 51.

This explanation is quite consistent with the observed phenomena, and Itacolumyte differs from other flexible rocks in the fact that its power of bending is not due to the flexibility of its constituent minerals, but to the existence of spaces round its quartzitic grains, in which a certain amount of motion is possible.

In flexible limestones, etc., the quality is due to the presence of fibres of asbestos, or plates of mica, which hold the particles of the rock together. The question-What is the true matrix of the diamond? yet remains unanswered; but all that we know of Itacolumyte dispels the idea that they are in anywise associated.