MAGNETITE . \IINKT ROCKS COUL80N. 

 TABLE II. 



283 



TABLE III. 



2. DESCRIPTION OF ROCK SPECIMENS. 



No. 765. This is a dark, heavy, and fine grained rock, composed of a mass of 

 magnetite, hematite, and quartz, through which run bands of quartz and minute 

 hematite flakes. Small fragments of the rock are strongly magnetic. Its specific 

 gravity is 3-97, the highest for the group. 



Microscopically, the quartz occurs in very fine grains, which show strain 

 polarisation colours and which contain myriads of inclusions of micaceous hematite or 

 " eisenglimmer." While eisenglinmier occurs abundantly within the quartz bands, 

 magnetite is the chief constituent of the rock. The structure is granoblastic and the 

 texture is schistose. The rock is a Magnetite-Schist. 



No. 926. This is a dark greasy-looking rock, extremely fine grained and 

 possessing a well-developed crystallisation-schistositA . 



Biotite is one of the chief constituents, occurring in very minute flakes and 

 showing no trace of any alteration to chlorite. Magnetite is fairly abundant and with 

 quartz makes up the bulk of the remainder of the rock ; it is usually xenoblastic in 

 form and generally of small dimensions. Quartz shows strain polarisation and contains 

 minute inclusions of magnetite, and epidote. This latter mineral is disseminated through 

 the rock in minute roughly circular grains. Calrite occurs in moderately large masses 

 and surrounds epidote, quartz, magnetite and biotite ; the characteristic cleavage is 

 well developed. The structure is lepidoblastic to granoblastic and the texture is 

 schistose. The rock is a Biotite-Magnetite-Srlii.tf. 



No. 576. This is a gneissic type in which magnetite, epidote, biotite, quartz, and 

 pink orthoclase can be recognised in the hand specimen. The structure is heteroblastir. 

 Magnetite is important and occurs in xenoblastic individuals with a roughly parallel 

 alignment. Garnets are rare; they cannot be recognised in the hand specimen and 

 are confined to certain bands in the section. Such as are present are the fragmentary 



