962 THE GEOLOGY OP MINNESOTA. 



[Leucoxene. Rutile. Garnet. Staurolite. 

 Zircon. Fluorite. 



autonomy by reason of which it not only quickly acquires its idiomorphic outlines 

 and remains small, thrusting aside all other elements, but it seldom embraces any 

 other minerals in a poikilitic manner. Yet it is observable, in numerous instances, 

 that it gives way to the outlines of other minerals. In one instance (No. 19H), it 

 was noticed in a dioryte that it was secondary to hornblende, which not only deeply 

 indented its margin, but was enclosed in it in the form of several isolated grains. 

 In No. 1515 it surrounds apatite and apparently some feldspar. 



Sphene occurs in nearly all the crystalline rocks except the oldest greenstones, 

 whether igneous or metamorphic, and especially in those with considerable amounts 

 of the dark silicates. It is also found in the clastic rocks, apparently as detrital 

 grains. 



Leucoxene represents that form of the alteration product of ilmenite or titanif- 

 erous magnetite which is most common in the original basic rocks and in the green 

 schists when they have partially decayed (Nos. 567, 1021, 1022). It is apparently 

 amorphous and remains in this state till metamorphic action recrystallizes it, when 

 it assumes the crystalline characters that are more definitely and usually designated 

 sphene. 



Entile is characteristically a mineral of the crystalline and subcrystalline schists, 

 appearing sometimes in clay slate (No. 395). It favors those rocks in which also 

 exists quartz. It likewise is apparently wholly a secondary mineral, resulting from 

 the recrystallization of the alteration products of ilmenite or of sphene after the 

 abstraction of the lime. The so-called sagenite net of rutile was observed in Nos. 

 422, 567, 896, 1750, 1814. Twinned rutile was noted in a chlorite schist at Tower, 

 in No. 869, and in an altered or contacting diabase at Wauswaugoning bay (No.. 265). 



Garnet is one of the metamorphic minerals of the Pewabic quartzyte at Chub 

 (Akeley) lake (No. 1895) and of the mica schists at Little Falls and Pike rapids 

 (Nos. 1670-1673) and occasionally of granite (No. 2189). 



Staurolite likewise is found abundantly in the metamorphic rocks at Pike rapids 

 and elsewhere in Morrison county (No. 849 and Mus. Reg. No, 2689). In an altered 

 state it was identified at the contact zone of Animikie slate with a diabase intrusive 

 (No. ). 



Zircon is a mineral of the intensely modified elastics under the action of basic 

 intrusion where gases and solutions were quick to penetrate (Nos. 552,1902); it also 

 is found in later detrital rocks and gravel. 



Fluorite is a constituent of granite at Saganaga lake (No. 2046), and was found 

 in connection with the Keweenawan basic rocks in their contact relations with 

 Animikie, and in veins in the Keweeuawan (No. 64A) and in the Archean granite 

 (No. 318). 



