OCCLUSION OF IGNEOUS ROCK 413 



show cleavage traces. Interference colors brilliant yellow of 

 First Order to greenish blue of Second Order ; (= r. Maxi- 

 mum extinction i6° and wavy. In convergent light, emergence 

 of a negative acute bisectrix is indicated. Inclusions of pleonaste 

 sometimes occur, arranged as if the amphibole represented orig- 

 inal grains of bronzite. 



A secondary form of amphibole is also found, mostly color- 

 less (tremolite), sometimes pale greenish or bluish (actinolite), 

 with distinct pleochroism, greenish white to colorless or bluish 

 white to pale salmon. It occurs in short prisms, elongated 

 scales, or slender fibrous blades, with cross partings, to i mm. 

 in length, with good relief. They may be gathered in clusters 

 or radial groups, or loosely scattered, and may also occupy inter- 

 spaces of the bar structure. Bright interference colors from 

 yellow of First Order to greenish blue of Second Order. Ex- 

 tinction generally parallel or at angle of 45° to the fibers and 

 wavy, but varies up to 22°. Some grains twinned, with extinc- 

 tion angle about 18°. In convergent light, the emergence of 

 an optic axis appears, with three colored rings. Double refrac- 

 tion negative. Along their margins the crystals are often col- 

 ored brownish red and yellowish brown by iron ochre. Many 

 are seen to pass into yellow serpentine, and some of the longer 

 blades into talc. 



Bronzite appears in allotriomorphic colorless grains, with 

 marked relief, usually mingled with scales of bastite and altered 

 amphibole. It is generally full of irregular fractures and clefts, 

 as by crushing, but in a few instances shows an eminent cleav- 

 age parallel to the brachypinacoid, 00 Poo (oio). In some 

 fragments a slight pleochroism was detected, greenish to yel- 

 lowish white. Extinction imperfect in the granular form, par- 

 allel in the compact, sometimes diagonal and wavy. Double 

 refraction positive. Granules of chromite and pleonaste ar- 

 ranged as original inclusions in this mineral. A peculiar kind 

 of alteration is shown in some thin sections by passage into 

 milky white, nearly opaque material. 



Many broad scales, finely fibrous, 1-3 mm. across, were 

 referred to bastite. These are reddish or brownish white and 



