MINERALOGY AND PETROLOGY. 947 



Tourmaline. Apatite. Barite. Calcite.] 



Tourmaline, which indicates the near action of volcanoes, containing boracic 

 acid and sometimes lithia, with varying amounts of magnesia, soda and iron, is 

 primarily a silicate of alumina. It has been found in microscopic crystals in the 

 greenstones and in Archean schists, as follows: Nos. 395 in clay slate, 473 in gray- 

 wacke, 737 in conglomerate, and 2162 in a quartz schist. It cuts the quartz in a vein 

 in No. 352. It is in syenyte in No. 993, in quartz-porphyry in No. 2237, and in gabbro 

 in No. 773. It occurs in the Pokegama quartzyte, base of the Animikie, at Pokegama 

 falls, No. 1525(a), and in the quartzyte and black slate of the Animikie in No. 1852. 



Apatite. The occurrence of this mineral in greater abundance along the zone 

 of contact of the Keweenawan basic eruptives on the elastics than elsewhere in the 

 state, so far as known, is indicative of the causes that have promoted its origin. In 

 these situations it is always idiomorphic. It is sometimes surrounded by hornblende 

 and sometimes by orthoclase or by quartz, and these are all secondary minerals in 

 the broader sense of that term, as already defined, and result from the transference 

 of the acid elements into the basic rock. Apatite resembles sphene in the vigor 

 with which it asserts its crystalline boundaries. Wadsworth has contended that 

 apatite in these conditions is secondary, and the writer is inclined to indorse 

 that view, but from different considerations. It is customary to place apatite 

 amongst the earliest of the phenocrysts to appear in a magma when cooling. 

 This is probably true of acid magmas (Nos. 858, 1025A, 1032, 1061, 1094, 2215), 

 to which the larger crystals of magmatic apatite appertain, but it has but little 

 application to basic magmas, because apatite is generally not found in them 

 except at contact zones, where it has apparently been produced by endomorphism 

 from the older rocks (Nos. IB, 5, 459, 512, 531, 595, 540, 789, 1684, 1685A, 1802). 

 When it is seen in the Archean granite (No. 368G) or dioryte in large crystals, it 

 is likewise idiomorphic, and appears to have been one of the earliest crystals 

 to form from the acid magma (Nos. 425, 805, 339B). Such crystals are, however, 

 nearly always much worn, or " corroded " at the angles, and they may have been of 

 still earlier date, i. e., they may have been grains of clastic origin deposited in the 

 debris from whose recrystallization the granite is supposed to have been formed. 

 Such clastic apatite occurs in rocks Nos. 311,2262, 366H. Apatite occurs sometimes 

 in diabase (Nos. 221, 1076). 



Barite is known to occur only in some veins that cut the quartzytes and slates 

 of Pigeon point (Nos. 272, 288A and 288B), where it constitutes a large percentage of 

 the vein matter. 



Calcite, besides forming the chief constituent in many veins (Nos. 272, 423) and 

 the filling of much amygdaloid, exists in microscopic particles in most of the clastic 

 greenstones (Nos. 1015, 1018, 1068), in the gray wackes (Nos. 473, 494), in the quartz- 



