Although the number of green-coloured minerals is large, but few of them are suitable for painters’ colours, because they occur so rarely in Nature that their employment for this purpose is out of the question, more especially since a very large number of green pigments can be obtained by artificial means. The most important of the earth colours in this category are Celadon green, or green earth, and malachite green--the latter, however, less so, because the substance of which it is composed can be prepared artificially. GREEN EARTH, OR CELADON GREEN This mineral is of a peculiar green colour, and the name “Celadon green” has been universally adopted in the nomenclature of colour shades. Green earth occurs native in many places, being the decomposition product of an extensively distributed mineral, augite, crystals of which are found in many of the deposits. The green earth of Monte Valdo, on Lake Garda (Upper Italy) has been used for a very long time as a pigment. It is chiefly prepared in Verona for distribution in commerce, and from this circumstance has acquired the name “Verona green,” or “Verona earth.” The earth is also found in Cyprus and Bohemia, where it frequently occurs as the decomposition product of basaltic tuff. However, whether obtained from Monte Valdo or elsewhere, the product is always placed on the market as Verona earth. Native green earth is always tough, mostly occurring in amygdalous lumps, but occasionally in the crystalline form of augite. It has a fine-grained fracture, a hardness between 1 and 2, and a sp. gr. between 2·8 and 2·9. The colour is not always quite uniform, pure lumps having the characteristic Celadon green appearance, whilst impure lumps are olive green to blackish green. In chemical composition it is chiefly ferrous silicate, and this compound must be regarded as the actual pigmentary principle of green earth. In addition, it contains varying quantities of other compounds which influence the depth of shade of the product. Verona earth chiefly consists of ferrous oxide in combination with silica; alumina, magnesia, potash, soda and water being also present. Analysis shows it to contain: ferrous oxide, 21%; silica, 51%; magnesia, 6%; potash, 6%; soda, 2%; and water, 7%. The green earths from Gösen, Atschau and Männelsdorf, near Kaaden (Bohemia) and the Giant’s Causeway (Ireland) have the following composition: +---------------+----------+----------+ | | Kaaden. | Giant’s | | | | Causeway.| +---------------+----------+----------+ |Silica | 41 | 56·4 | |Alumina | 3 | 2·1 | |Ferrous oxide | 23 | 5·1 | |Ferric oxide | -- | 14·1 | |Lime | 8 | -- | |Magnesia | 2 | 5·9 | |Potash | 3 | 8·8 | |Carbon dioxide | 19 | -- | |Water | -- | 6·8% | +---------------+----------+----------+