In the works of Bauer, Rosenbusch, Weinschenk, Schilling and Iddings will be found accounts of a mineral named ‘Hussakite.’ These accounts rested on the work of Kraus and Reitinger,[112] who in 1901 announced the discovery of a new species. The crystals were obtained as a specimen of xenotime by Prof. Muthmann from Dr. E. Hussak, in São Paulo, and had the crystallographic properties of that mineral. On analysis, the amount of sulphur trioxide present was found to be remarkably high (6·3 per cent.), and Kraus and Reitinger concluded that the substance was distinct from xenotime. They announced it as a new mineral, with the name Hussakite, and the formula 3R₂O₃,3P₂O₅,SO₃ or 6RPO₄,SO₃, and stated that by the action of dilute alkalies the sulphur trioxide could be easily and completely removed. They therefore regarded xenotime as a pseudomorph[113] after hussakite, the sulphur trioxide having been removed from the latter by the action of the alkaline waters of the earth’s crust. In support of this view, they gave analyses of opaque crystals from a Bahia sand represented as containing 2·6 to 2·7 per cent. of sulphur trioxide, and so as being intermediate forms produced during the change. [112] _Zeitsch. Kryst. Min._ 1901, ~34~, 268. [113] One mineral is said to be pseudomorphous after another when the first is produced from the second by a chemical change which proceeds so slowly that the original structure and crystalline form are unaltered (_i.e._ a change proceeding molecule by molecule). The pseudomorph is usually opaque and shows clear signs of the alteration. The latter conclusion was quickly challenged by Brögger, who found no sulphur trioxide in a perfectly fresh and transparent xenotime from Åro in Scandinavia. Brögger concluded that the Hussakite of Kraus and Reitinger was an independent species of the formula 5YPO₄,(YSO₄)PO₃, and that xenotime was not derived from it. Basing his work on the barium chloride test given by Kraus and Reitinger (see below) Rösler[114] declared that ‘Hussakite’ was a common accessory constituent of igneous rocks, having been previously mistaken for zircon, which it resembles in appearance and optical properties. [114] _Zeitsch. Kryst. Min._ 1902, ~36~, 258.