450 W. T. BRIG HAM ON THE VOLCANIC PHENOMENA 



covered with four feet of earth and about a foot of good soil, the crystals being near the 

 bottom of the bed which was cut away to form a roadway. 1 The most* common form is 

 milky quartz stained with oxides of iron, found on Molokai and Kauai. I have never seen 

 this form from the other islands, although it doubtless occurs. 



Aivjitc. 



Augite is the common constituent of all the recent Hawaiian lavas, but it is only in the 

 tufa cones that crystals of any size occur. The variety termed Palagonite by Von Walters- 

 hausen is common at Leahi, Koko, and Aliapaakai, where the rather rough crystals are 

 imbedded in the tufa, and seem to be broken and worn. The Hawaiian specimens have not 

 been analyzed, but the composition of this variety is so remarkably uniform that I quote 

 the analyses of Von Waltershausen. 



Chrysolite. 



This mineral is very common in most of the lavas that have issued low down the flanks 

 of the mountains. On the summit no traces are found in the massive clinkstone which 

 forms the crater walls. In the flow of 1840 from Kilauea the a-a is full of it, and where the 

 stream entered the sea the matrix was so pulverized that the chrysolite was set free and is 

 now washed up in the clefts of the rocky shore as a green sand or gravel. The larger grains 

 are amorphous, half an inch in diameter, while the smaller sand is used in mortar for fire- 

 bricks. At Aliapaakai fine spheroidal masses, sometimes four to six inches in diameter, are 

 found, and in these the grains seem to be flattened against each other. T found chrysolite in 

 some scoria3 on the top of Hualalai, and in a lava of ancient date in Kilauea. It is not 

 uncommonly altered by the oxidation of the iron into a red and softer mineral. It is found 

 changed to a red color in cellular basalt on Oahu containing Thompsonite. 



Garnet. 



Only two specimens of garnet were seen, both at the summit of the cliff at Aliapaakai. 

 The crystals were dark red, a quarter of an inch in diameter, dodecahedrons, with the edges 

 truncated by the planes of a tetragonal triakis-octahedron. 



Biotite. 



A few small tabular hexagonal crystals, nearly black, with a submetallic lustre, were found 

 imbedded in the tufa at Aliapaakai. 



Labradorite. 

 It is not uncommon in the crater of H;tleakala, also on Mauna Loa, where it occurs in 



1 Quartz crystals, with perfect pyramidal faces at both ends of the crystal, were found in trachyte in the Andes of Bolivia, 

 by Forbes. Quart. Journ. Geol. Soc, xvii., pp. 26 and 29. 



