DIAMOND: OCCURRENCE IN BRAZIL 177 



during which the mines were under Government management, only eighty stones exceeding 

 an oitava ( = 171 carats) were secured by rightful owners ; what may have been stolen is, 

 of course, not known. 



The largest Brazilian diamond is the "Star of the South," or "Southern Star" 

 (Fig. 48), which was unearthed in the fifties at Bagagem. In its rough condition it weighed 

 2541 carats, and when cut as a brilliant 125 carats. A stone of 138J carats was found in 

 the Rio Abaete, and one of 120f carats in the Caxoeira Rica near Bagagem, while one of 

 107 carats was reported from Tabacos on the Rio das Velhas. No other stones exceeding 

 100 carats have been heard of. The famous " Braganza " of the Portuguese crown jewels, 

 a reputed diamond as large as a hen's egg and weighing 1680 carats, is probably only a 

 pebble of transparent, colourless topaz ; accurate information on the subject cannot, how- 

 ever, for obvious reasons, be obtained from the Portuguese Government. 



The crystalline form of Brazilian diamonds is by no means constant, varying in 

 stones from different districts. Moreover, stones from different localities are not equally 

 regular in form, those from the Cincora district, for example, being more distorted and 

 misshapen than stones from Minas Geraes or Salobro. 



Generally speaking, the principal forms for all localities are the rhombic dodecahedron 

 and the hexakis-octahedron, both having rounded faces and often deviating considerably 

 from the ideal form (Fig. 31, c to J\) The octahedron, which is rare, is also frequently 

 distorted, sometimes appearing in the form of triangular plates. The predomination of 

 cube faces (Fig. 31 a) is especially characteristic of Brazilian crystals ; such forms are very 

 fi-equent here, but rare in other countries. The tetrahedron and other hemihedral forms, 

 especially the hexakis-tetrahedron (Fig. 31 h), are only rarely found; twinned rhombic 

 dodecahedra (Fig. 31 h) occur frequently ; twinned octahedra (Fig. 31 g) are, on the other 

 hand, rare. 



Irregular intergrowths of diamond crystals are frequently met with ; indeed the famous 

 " Star of the South " formed part of such an intergrowth, since its rough surface showed 

 several impressions of smaller diamonds. Nodules of bort occur not infrequently ; often they 

 are almost perfectly spherical in form (Plate I., Fig. 3), the surface, however, being rough 

 owing to the projection of the corners of the small octahedral crystals which build up the 

 radial aggregate. On the whole, about one-fourth of Brazilian stones are useless as gems ; 

 these are also described as "bort " and are applied to technical purposes. 



The surface of a rough diamond, that is of the natural crystal, is either smooth and 

 shining, or rough, striated, and dull. Rough stones are usually opaque or translucent, but 

 are sometimes completely transparent ; in the latter case they exhibit a fine play of 

 prismatic colours, such as is usually only apparent after cutting. The peculiar surface 

 lustre, characteristic of stones from Matto Grosso, has been previously mentioned ; it is found 

 on no other Brazilian diamonds. Diamonds penetrated in all directions by cavities, so that 

 their structure comes to resemble that of pumice-stone, are occasionally met with. 

 Regularly formed depressions may sometimes be seen on the surface of a crystal ; very 

 frequently these depressions have the shape of crystals of quartz and must have been formed 

 by the diamond resting during its growth on a quartz crystal. Diamond crystals showing 

 evidences of contact with other minerals have been often described ; the " Star of the 

 Soutli '"■ (Fig. 48) is undoubtedly such a crystal, the broad under surface being very probably 

 the area by which it was attached to the parent rock. 



The colour and the qualities depending on this feature vary considerably, differing in 

 different localities. About 40 per cent, of Brazilian diamonds are completely colourless and 

 of these 25 per cent, are of the purest water and the first quality, the beautiful and highly 



M 



