A NEW MINERAL

Ashburton Guardian, Volume 53, Issue 133, 17 March 1933, Page 8

A NEW MINERAL

PRACCITE FOUND. X-RAY ANALYSTS. A new mineral has recently been discovered by the employment of X-ray analysis. Tn honour of the contributions of ISir William Bragg and Professor W, L. Bragg to the technique of X-ray analysis/ this metal has been named "braggite;" The methods of determining the structure of substances of X-ray analysis are able to reveal a crystalline structure in substances not suspected of being crystalline from superficial appearance. In fact, the X-rays have shown that nearly all substances are built of crystals; the metals, and even such substances as hair fibres, are examples. Besides revealing the crystalline property of sumstances, the X-rays may reveal the arrangement of the atoms within the constituent crystals, and they may thus give all this knowledge from a specimen of material no bigger than a pin's head. The possibility of using X-rays to identify rare or hitherto unknown minerals may thus be appreciated, says a writer in the "Manchester Guardian." The first successful use of X-ray analysis in the discovery of a new mineral, braggite, is at inresent chiefly of scientific interest. The particular mineral discovered is not of great economic importance. But in the future X-ray analysis may be used to make economically important discoveries. For instance, a rare mineral may be important, not for itself, but for the company it keeps. It may act as a pointer to the probable presence of unsuspected minerals of greater economic importance. Chemical Importance. Braggite is a compound of palladium, a metal resembling platinum. Like platinum, palladium is a powerful catalyst. For example, hydrogen and oxygen will combine at ordinary room temperature to form water if a piece of palladium foil is placed ini the container. This quality consequently makes the metal important in the chemical industry. In another way, braggite is a distorted form of the platinum mineral cooperite—one in which atoms of palladium have been substituted for atoms of platinum. Braggite was found in specimens of what was thought to be cooperite, which were sent to the British Museum from the platinum-bearing rocks of the Bushveld, ini the Transvaal. The examination of these specimens with. X-rays by Sir F. A. Bannister and others showed that they contained three sorts of crystals, so they were separated into three little heaps according to the crystal structure revealed by the X-rays. Then each heap was analysed chemically by Mr Hey. The first proved to be ruthenium sulphide, the second was platinum sulphide. The name "cooperite" was reserved for this second heap because its composition was nearest to that originally given by Cooper to his mineral. The third heap contained platinum, sulphur, palladium, and a little nickel. It differed from the second heap in containing some palladium, and its crystal structure was also different. ' How it is Formed. Apparently braggite is formed from pure cooperite (platinum sulphide) by a replacement of some of the platinum atoms by palladium atoms. As the palladium atoms are rather smaller than platinum atoms this cannot proceed beyond a certain degree without a in the general arrangement of the'atoms within the crystal. If too many palladium atoms are introduced the structure of the crystal is weakened, until it collapses, and the constituent atoms rearrange themselves in a more stable and quite different way. The Bushveld deposits in the Transvaal have yielded specimens of all the known compounds of the platinum metals, and a number of fragments have given X-ray photographs which have not vet been identified.