JAROSITE

jarosite, a rare mineral species consisting of hydrous potassium and aluminium sulphate, and belonging to the group of isomorphous rhombohedral minerals enumerated below:-- alunite k2 [al(oh)2]6 (so4)4 jarosite k2 [fe(oh)2]6 (so4)4 natrojarosite na2 [fe(oh)2]6 (so4)4 plumbojarosite pb [fe(oh)2]8 (so4)4 jarosite usually occurs as drusy incrustations of minute indistinct crystals with a yellowish-brown colour and brilliant lustre. hardness 3; sp. gr. 3.15. the best specimens, consisting of crystalline crusts on limonite, are from the jaroso ravine in the sierra almagrera, province of almeria, spain, from which locality the mineral receives its name. it has been also found, often in association with iron ores, at a few other localities. a variety occurring as concretionary or mulberry-like forms is known as moronolite (from gr. [greek: moron], "mulberry," and [greek: lithos], "stone"); it is found at monroe in orange county, new york. the recently discovered species natrojarosite and plumbojarosite occur as yellowish-brown glistening powders consisting wholly of minute crystals, and are from nevada and new mexico respectively. (l. j. s.) jarrah wood (an adaptation of the native name _jerryhl_), the product of a large tree (_eucalyptus marginata_) found in south-western australia, where it is said to cover an area of 14,000 sq. m. the trees grow straight in the stem to a great size, and yield squared timber up to 40 ft. length and 24 in. diameter. the wood is very hard, heavy (sp. gr. 1.010) and close-grained, with a mahogany-red colour, and sometimes sufficient "figure" to render it suitable for cabinet-makers' use. the timber possesses several useful characteristics; and great expectations were at first formed as to its value for ship-building and general constructive purposes. these expectations have not, however, been realized, and the exclusive possession of the tree has not proved that source of wealth to western australia which was at one time expected. its greatest merit for ship-building and marine purposes is due to the fact that it resists, better than any other timber, the attacks of the _teredo navalis_ and other marine borers, and on land it is equally exempt, in tropical countries, from the ravages of white ants. when felled with the sap at its lowest point and well seasoned, the wood stands exposure in the air, earth or sea remarkably well, on which account it is in request for railway sleepers, telegraph poles and piles in the british colonies and india. the wood, however, frequently shows longitudinal blisters, or lacunae, filled with resin, the same as may be observed in spruce fir timber; and it is deficient in fibre, breaking with a short fracture under comparatively moderate pressure. it has been classed at lloyds for ship-building purposes in line three, table a, of the registry rules.