SENFT ON ROCKS. 7 



1 . With white, yellow-white or reddish-white, rose-red, greyish- 

 brown, or reddish-brown orthoclase, or, instead, oligoclase or albite, 

 as the chief constituent ; with it are combined quartz, mica or talc, 

 and eleeolite or hornblende. Accessory constituents : garnet, tour- 

 maline, zircon, iron-pyrites, and titanite. Colour : whitish, reddish, 

 grey- or red-brown. Texture : distinct. Weathering : white, yellow, 

 or clayey. [2. Group. Orthoclasite (granite-rocks). Pitchstone- 

 porphyry, felsit-porphyry {with or without quarts), granite and pro- 

 toyine, syenite and sircon-syenite, myascite, granulite, and gneiss .] 



2. Mica or talc is the chief constituent, or, instead, occasionally 

 damourite ; mixed with it are quartz-grains or granular limestone. 

 Texture : foliaceous. Accessory minerals : chiefly garnet and tour- 

 maline (by taking up orthoclase, it passes into Group 2). Weather- 

 ing : ferruginous, and loamy. [3. Group. Stilpnolite (mica-rocks). 

 Mica-slate (paragonite and iron-mica-slate), calc-mica-slate, and 

 talc-mica-slate .] 



3. Quartz as the chief constituent, in combination with mica and 

 talc, or with schorl and topaz. Whitish-grey and dark-grey. Tex- 

 ture : granular or thick-slaty. Accessory constituents : Orthoclase, 

 tin-ore, and mica. [Group 4. Quartzite. Quarts-slate, itacolumite, 

 greisen, and schorl-rock (and top as -rock.)'] 



4. Blackish-green or black hornblende as chief constituent, com- 

 bined with white or greenish- white albite. Mixture : distinct or in- 

 distinct. Texture: granular, slaty, dense, and porphyritic. Ac- 

 cessory constituents : quartz, mica, iron- and magnetic-pyrites. 

 Colour : grey-green, black with white, or grey with red. Weather- 

 ing : dirty white, grey, or greenish-yellow, and clayey. [Group 5. 

 Amphibolite (diorite) . Diorite (ophite, norite, nodular diorite, and 

 diorite-slate), and diorit-porphyry (and epidosite). 



II. Order. Labradorite. Rocks containing labradorite, but without 

 orthoclase or quartz. Essential constituents : labradorite or oli- 

 goclase, nephelin, leucite, hypersthene, diallage, augite, titani- 

 ferous magnetic iron-ore. Colour : greyish-green to black. Ac- 

 cessory constituents : iron-pyrites, talc, chlorite, calc-spar, zeolite, 

 and olivine. Mixture : often indistinct. Always partly decom- 

 posable in sulphuric acid ; losing water and becoming lighter on 

 heating. 



1. Suborder. Mostly decomposable in hydrochloric acid. On 

 heating to redness in a tube, become lighter. Essential consti- 

 tuents : labradorite, or, instead, saussurite ; besides^ hypersthene, 

 diallage, augite, iron-chlorite, and calc-spar. Distinctly and in- 

 distinctly mixed. 



a. Rocks containing pyroxene and diallage (chlorolites) . 

 1. Undecomposable in hydrochloric acid. Grass-green, greenish- 



orey, or greenish-brown diallage or bronze-coloured hypersthene as 



chief constituent, combined with labradorite, saussurite, or garnet. 



Accessory constituents : strahlstein, magnetic pyrites : no calc-spar 



