30 PROCEEDINGS OF THE ISTATIONAL MUSEUM vol.71 



CHLORITES 



Several varieties of chlorite were seen in different specimens in this 

 collection. Minute globules and aggregates of globules of a smoky- 

 gi-ay chloritic mineral occur on epidote, adularia, and titanite in 

 the andradite specimens (No. 845G0). The chlorite appears to be 

 the youngest mineral of the specimens except pyrite. 



A single flat specimen (No. 84570) consists largely of ill-defined 

 inelastic blackish-green scales up to 3 millimeters across. Under the 

 microscope these are mostly blue-green in basal plates but in con- 

 siderable part they are oxidized to brownish-green. The few grains 

 which could be turned on edge did not seem markedly pleochroic. 

 The mineral is uniaxial and negative with the w refractive 

 index=1.60. This may be biotite but it looks more like a chlorite. 



A single specimen shows numerous plates up to 1 centimeter 

 across (No. 84570) of pale apple-green chlorite embedded in coarse 

 calcite. These show repeated twinning on the same law which pro- 

 duces the common "A" or feather structure in mica. Under the 

 microscope the material of these crystals is practically uniaxial and 

 optically positive with an index of oj=1.578. This is probably 

 penninite. 



A piece of banded rock, probably altered shale (No. 84571) is 

 coated on one side with a druse of micaceous crystals up to 1 milli- 

 meter in diameter. These are hexagonal-prismatic with perfect 

 micaceous cleavage. The prism faces are corroded and dull but the 

 luster on the base is pearly and somewhat iridescent. Optically this 

 mineral is biaxial and negative with 2V small to very-small, acute 

 bisectrix (X) inclined slightly to the normal to the cleavage, indices, 

 /?= 1.570, This is probably an iron-free chlorite. 



MIZZONITE 



Scapolite, all apparently of the variety mizzonite, makes up the 

 bulk of a large number of specimens. The most striking lot of these 

 (No, 84567—6 specimens) consists of large variously oriented pris- 

 matic masses or sheaves up to 4 by 10 cm, of ill-defined slightly 

 divergent fibrous structure. This material varies from slightly 

 purple to cream color where not stained by iron. The interstices 

 between the masses of scapolite are filled with white calcite. Under 

 the microscope the material of the scapolite masses, which under a 

 lens appears pure, is found to consist of 3 minerals. The scapolite 

 itself is in part clear and glassy, uniaxial and negative ( — ) with 

 indices of refraction approximately er=1.535, w=1.551— 1.555, indi- 

 cating mizzonite. This mizzonite exhibits alteration or replacement 



