Nephrite, or true jade, may be regarded as a finely fibrous or compact variety of amphibole, referred either to actinolite or to tremolite, according as its colour inclines to green or white. Chemically it is a calcium-magnesium silicate, CaMg3(SiO3)4. The fibres are either more or less parallel or irregularly felted together, rendering the stone excessively tough; yet its hardness is not great, being only about 6 or 6.5. The mineral sometimes tends to become schistose, breaking with a splintery fracture, or its structure may be horny. The specific gravity varies from 2.9 to 3.18, and is of determinative value, since jadeite is much denser. The colour of jade presents various shades of green, yellow and grey, and the mineral when polished has a rather greasy lustre. Professor F. W. Clarke found the colours due to compounds of iron, manganese and chromium. One of the most famous localities for nephrite is on the west side of the South Island of New Zealand, where it occurs as nodules and veins in serpentine and talcose rocks, but is generally found as boulders. It was known to the Maoris as _pounamu_, or "green stone," and was highly prized, being worked with great labour into various objects, especially the club-like implement known as the _mere_, or _pattoo-pattoo_, and the breast ornament called _hei-tiki_. The New Zealand jade, called by old writers "green talc of the Maoris," is now worked in Europe as an ornamental stone. The green jade-like stone known in New Zealand as _tangiwai_ is bowenite, a translucent serpentine with enclosures of magnesite. The mode of occurrence of the nephrite and bowenite of New Zealand has been described by A. M. Finlayson (_Quart. Jour. Geol. Soc._, 1909, p. 351). It appears that the Maoris distinguished six varieties of jade. Difference of colour seems due to variations in the proportion of ferrous silicate in the mineral. According to Finlayson, the New Zealand nephrite results from the chemical alteration of serpentine, olivine or pyroxene, whereby a fibrous amphibole is formed, which becomes converted by intense pressure and movement into the dense nephrite. Nephrite occurs also in New Caledonia, and perhaps in some of the other Pacific islands, but many of the New Caledonian implements reputed to be of jade are really made of serpentine. From its use as a material for axe-heads, jade is often known in Germany as _Beilstein_ ("axe-stone"). A fibrous variety, of specific gravity 3.18, found in New Caledonia, and perhaps in the Marquesas, was distinguished by A. Damour under the name of "oceanic jade."