The mineral which forms the subject of this communication came from the gem mines of Rakwana, Ceylon, and was brought to England by Mr. Joseph Baddeley, who, while superintending operations there, had formed a collection representative, it was believed, of almost every kind of pebble to be found at the works. This collection Mr. Baddeley, on his return home, submitted to Mr. Pringle at the Museum of Practical Geology, London. In looking, from time to time, over the collection, Mr. Pringle had occasion to take the specific gravity of some of the specimens. Amongst those so tested were certain pebbles the sp. g. of which was found to be about 3.98. This resuIt, combined with their other physical characters, having rendered it impossible for Mr. Pringle to assign them to spinel, ilmenite, or other species with which he could compare them, he handed the pebbles over to me for chemical analysis.