THE PYROXENE AND AMPHIBOLE GROUPS (HYPERSTHENE) 451 



THE PYROXENE AND AMPHIBOLE GROUPS. 



HYPERSTHENE (with Bronzite, Bastite, and Diallage). 



In this class are included those members of the pyroxene or augite group of minerals, 

 which exhibit on one particular face a peculiar metallic sheen, and which depend on this 

 feature for their application as ornamental stones. 



HYPEBSTHENE. 



Hypersthene is remarkable for the display of a magnificent copper-red, metallic sheen, 

 which shows up very effectively against the dark body-colour of the mineral. It is much 

 esteemed as an ornamental stone, especially in France, but when the sheen is absent, as is 

 sometimes the case, the mineral has no other feature of beauty, and is useless for decorative 

 purposes. 



The finest material comes from the coast of Labrador, and this is used, probably 

 exclusively, for cutting as gems. The small island of St. Paul is often mentioned as a 

 locality, and for this reason the mineral is also referred to as paulite, while lapidaries know 

 it as " Labrador hornblende." It is associated here with labradorite, famous for its coloured 

 sheen, and, as described above, the two together form rock-masses of considerable size. 

 What has been said respecting the occurrence and distribution of labradorite in this region 

 holds good also for hypersthene. The amount of material found here is considerable, and 

 good specimens free from fissures can be easily cut out of the best portions of the larger 

 rock-masses. Being, thei-efore, comparatively abundant, hypersthene is not a mineral of 

 very great value. 



Chemically the mineral consists essentially of a silicate of magnesium with the formula 

 MgO.SiOg, but a considerable portion of the magnesia is replaced by an equivalent amount 

 of ferrous oxide. The following is an analysis of hypersthene from Labrador : 



Per cent. 



Silica (SiOj) 49-86 



Alumina (AljOj) . ... . 6-47 



2-25 

 14-11 



Ferric oxide (FcgOg) 

 Ferrous oxide (FeO) 

 Manganese oxide (MnO) 

 Magnesia (MgO) 

 Lime (CaO) . 



0-67 



24-27 



2-37 



100-00 



The mineral is one of the pyroxenes which crystallise in the rhombic system, but 

 distinct crystals are not found in Labrador. The water-worn masses in which hypersthene 

 occurs here are about the size of a man's fist, and exhibit more or less distinct cleavages and 

 planes of separation. One of these separation planes is specially prominent by reason of the 

 presence of innumerable crystalline plates embedded in the hypersthene. These plates or 

 scales are all arranged parallel to the separation plane ; they have a bright metallic lustre, 

 and possibly consist of brookite, a crystallised modification of titanium dioxide. The 

 tendency of the mineral to separate along this plane often gives rise to fissures in the stone, 



