78 LITHOLOGICAL GEOLOGY. 



early applied ; and also nephelinyte and amphigenyte, nephelite in the former, and 

 leueite in the latter replacing for the most part the labradorite. The term trap was 

 early applied in Sweden (from trappa, step) to the eompact columnar variety of basaltic 

 rock. 



(1.) Syenyte. For description see p. 69. 



(2) Hyposyexyte. For description see p. 70. 



(3.) Diory'te. (Greenstone.) For description see p. 70. A related rock has been 

 called propylyte, and a variety containing free quartz from Transylvania Dacite. 

 Andesyte, a rock consisting of hornblende with oligoclase or andesite, is closely related 

 to dioryte. 



(4.) Melaphyre (a name variously used; here restricted to the oligoclase kinds). 

 Crystalline-granular to cryptocrystalline. Dark gray to grayish, greenish and brown- 

 ish-black ; sp. gr. 2*65-2*90. Consists of oligoclase and pyroxene (augite), with some- 

 times disseminated grains of magnetite. Sometimes porphyritic or amygdaloidal. 

 Looks like doleryte, but has less density and contains more silica (55 to 62 per cent.). 

 Two kinds from the Harz (having G. = 2-71, and 2-78) afforded Streng— Silica 56-22, 

 57*72, alumina 15*56, 10*58, protoxyd of iron 8*07, 10*55, prot. manganese 0*00, 0-17, lime 

 6-36, 7-59, magnesia 5-97, 6-77, potash 3-29, 1-89, soda 2-40, 2-00, water 2.75, 1-70, car- 

 bonic acid 1-95, 3-56 = 102*57, 102 - 53. The name has been used, as well as diabase, 

 for a chloritic doleryte (see below). The variety of andesyte which contains augite, in 

 place of hornblende, is essentially the same in constitution with melaphyre. 



Trachya loleryte is near melaphyre, it consisting of oligoclase and hornblende, or 

 augite, with some magnetite; G. = 2*74-2*80. (From Teneriffe, Moravia, etc.) 



(5.) Doleryte. — Crystalline-granular to cryptocrystalline; dark gray to grayish, 

 bluish or greenish black, brownish, reddish; Sp. gr. = 2*75^3*2. Consists of labradorite 

 and augite, with usually disseminated grains of magnetite. Silica commonly 48 to 52 

 percent. A variety from Meissner (having G. = 2*75)affordedHeusser — Silica 48-00, 

 alumina 16"2S, protox. iron 15*55, lime 9*50, magnesia 3*85, potash 2-01, soda 2-01, 

 water and loss 2*80 = 100; and Rammelsberg makes it a mixture of 47*60 labradorite, 

 49*60 augite, with magnetite. The cryptocrystalline and scoriaceous variety is often 

 called basalt, and a gray fine-grained variety anamesite. 



Occurs porphyritic, having the labradorite in distinct crystals; amygdaloidal, contain- 

 ing small rounded or almond-shaped nodules; chloritic, owing to the presence of dis- 

 seminated chlorite arising from partial alteration, either through the action of moisture 

 gaining access while the ejection was in progress, or subsequently through infiltration; 

 scoriaceous, as in the common dolerytic lavas. Sometimes it is zeolitic as well as 

 chloritic, through alteration. 



Doleryte graduates into melaphyre through the presence of oligoclase in addition to 

 labradorite. Diabasyte (or Diabase) includes both metamorphic (p. 70) and eruptive 

 rocks; and to the latter section belong the weak-Iustred chloritic dolerytes. 



(6.) Peiudotyte. Of the color, specific gravity, and texture of doleryte, and hav- 

 ing the same constituents, with the addition of disseminated grains of chrysolite (olivine), 

 like green bottle-glass in color. Often called chrysolitic doleryte. Occurs porphyritic, 

 amygdaloidal, and scoriaceous. The last is a very common kind of lava. 



(7.) Amphigenyte. — Dark gray, fine-grained, and more or less cellular, constitut- 

 ing the lavas of Vesuvius and some other European volcanic regions. Sp. gr. 2*7-2*9. 

 Consists chiefly of leueite in place of most of the labradorite, along with augite and 

 some disseminated magnetite. The leueite is in disseminated grains or in 24-faced 

 crystals. Called also Leucitophyre. 



(8.) Nepheliny'te. — Crystalline-granular; ash-gray to dark gray ; resembling some- 

 what amphigenyte, but consisting chiefly of nephelite and augite, with some magnetite 

 in grains. The nephelite is partly in distinct crystals. 



Dolerytic (/lass, or obsidian, is a black glass often formed in volcanoes where the lavas 

 are doleryte or peridotyte. At Kilauea, the glass contains, according to Silliman, 22 to 

 30 percent, of protoxyd of iron, approaching the so-called fayalite, and iron- chryso- 

 lite. Tachylyte is a kind found with basalt, containing 55 per cent, of silica, 13 of 

 protoxyd of iron, etc. They are mixtures and not mineral species. 



