434 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



sheen. These uncoloured patches, especially those in the shape of strips, sometimes display 

 a coloured sheen when the stone is moved into another position relative to the incident 

 light and the eye of the observer, while at the same time the portions, which before were 

 colom-ed, now assume the dull grey body-colour of labradorite. On replacing the stone in 

 its original position these relations are reversed. Stones in which the sheen is interrupted 

 in this way are much less valuable than those which display a uniform sheen over the whole 

 reflecting surface : these latter are rare and always of small size. 



The value of labradorite increases with the depth and brilliancy of its coloured sheen. 

 Stones with a dusky sheen are referred to as " bull's-eyes " (ceil-de-bceiif), and do not fetch 

 very high prices. The value also depends to a certain extent upon the colour of the stone, 

 since some colour-varieties are less common than others. The price of perfectly faultless 

 stones is rather high, but is much less for less perfect examples. The best material is cut 

 for use as gems ; larger pieces of inferior quality are utilised in the manufacture of small 

 objects of various kinds, such as boxes, stick-handles, &c. It is customary, also, to make 

 use of labradorite in the representation of objects with a metallic colour, such as the wings 

 of butterflies in mosaics, and it is used for many other ornamental purposes. At the 

 beginning of the nineteenth century small reliefs representing a mandrill baboon were much 

 in vogue, and these were fashioned out of this stone in such a manner that only the snout 

 and the other parts of the body, which are coloured in the living animal, showed the 

 coloured sheen of the stone. 



The chatoyant colom-s of labradorite have been explained in various ways, and it is 

 possible that the yellows and greens and the blues are due to different causes. In the case 

 of yellow and of green, the chatoyant colours are caused by the inclusion of minute, brownish 

 translucent plates, of what appears to be haematite, magnetite, and ilmenite, in the substance 

 of the labradorite. These plates are rhombic, hexagonal, or quite irregular in outline, and 

 under the microscope are seen to be embedded in the felspar in great numbers and all 

 parallel to the surface from which the coloured sheen is reflected. The blue colour, on the 

 other hand, is not connected with the presence of enclosures, for it is sometimes very 

 prominent when enclosures are completely absent. We are probably dealing here with a 

 complicated optical phenomenon connected with the interference of light, for which a 

 complete explanation remains still to be sought. 



Labradorite was first discovered by Moravian missionaries among the Esquimaux of the 

 Labrador coast towards the end of the eighteenth century. The first stones were brought 

 to Europe in 1775, and specimens from Labrador were presented to the British Museum in 

 1777 by the Rev. Mr. Latrobe ; the largest is a slab measuring 'i feet by 1 foot. The 

 mineral forms one of the constituents of an igneous rock, pebbles and boulders of which are 

 widely distributed in this region. The other constituent is hypersthene, a mineral of the 

 augite group, with a fine copper-red, metallic reflection. The rock is very coarse-grained, 

 and in consequence it is unusual to find pebbles which contain the two constituents side by 

 side ; nearly always they are small and consist wholly of labradorite or of hypersthene. As 

 to the conditions under which the rock occurs in situ but little is known. The bay of 

 Nunaengoak, on the northern border of the mainland of Labrador, near Nain, is said to 

 abound in the so-called " labrador-rock." East of the mainland is the small Isle of Paul 

 (Tunnularsoak), which, especially in former times, was often referred to as a locality for 

 labrador-spar, while the principal locality has been stated to be an inland lake west of Nain. 

 Near this place the labradorite-hypersthene rock, which is known to petrologists as norite, 

 is said to occur in a very coarse-grained hornblende-granite, portions of which may be seen 

 attached to specimens preserved in collections. According, however, to other views, this 



