236 THE CRYSTAL FALLS IKON-BEARING DISTRICT. 



to get imx o])tical tests, except tliat of extinction, owing- to the minute size 

 of the inchisions and to the fact that where larg-e enough for examination, 

 the tests were vitiated b}' the presence of the hornblende. 



Of these inclusions some are readily distinguishable as rutile. Some 

 of the larger of the crystals reach a length of 0.045 mm. and a thickness 

 of 0.0125 mm. Numbers of them show the cliaracteristic heart-shaped 

 and geniculated twins of rutile, so that there is no doubt as to the determi- 

 nation. Associated with the rutile are other crystals 0.019 mm. long, which 

 show the typical pointed pyramidal development of octahedrite (anatase). 

 Still others show a flat tabular development somewhat similar to that of 

 brookite, though these could not be positively determined as that mineral. 

 The hexagonal plates of clove-brown color so frequent in hornblende and 

 also in hyperstheue occur also in this hornblende. They are believed to be 

 micaceous ilmenite. The thin plates are translucent, thicker ones are less 

 so, and those which are still thicker are opaque and metallic. The thin 

 plates appear when on edge as fine, hairlike streaks. The thick ones 

 appear in the same position as more or less rectangular bars or rods. Often 

 these small plates are associated with masses of iron oxide, also included in 

 the hornblende. This iron ore occurs in the plates and bars characteristic 

 for ilmenite. These ilmenite masses are translucent only on the edges, 

 where the slide has cut the mass in such a manner as io give an exceedingly 

 thin section of the ore. At such places the ore is transkicent with the 

 same brown color as the thin plates. Another rare variety of the inclu- 

 sions occurs in round grains of rich green color, and may possibly be a 

 spinel. 



In those sections in which both original brown and original green 

 hornblende occur the inclusions are confined to the brown kind. Where 

 the brown kind is surrounded by the green hornblende the inclusions grad- 

 ually diminish in quantity as we approach the green zone. With this goes 

 also, hand in hand, a lightening of the color of the including mineral 

 (brown hornblende), and there is thus an imperceptible change from the 

 brown to the green hornblende. Where the green hornblende occurs alone 

 it is frequently as full of inclusions as is the brown hornblende of other 

 sections. Individuals of the same sections differ from one another with 

 resjject to the quantity of the inclusions, some being crowded with them^ 

 while others are practically free from them. 



