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present, usually in well-shaped crystals, often zoned; orthoclase forms large irregular plates in which the other minerals are embedded. There is rarely any considerable amount of See also:

QUARTZ

quartz, though in a few of these rocks this See also:

MINERAL

mineral occurs (the quartz-monzonites). Other features are the abundance of See also:

AUGITE

augite, See also:

PALE (through Fr. pal, from Lat. palms, a stake, for paglus, from the stem pag- of pangere, to fix; " pole " is from the same original source)

pale See also:

green or brownish green, and of large See also:

BRONZE

bronze-coloured plates of See also:

BIOTITE

biotite which are of quite irregular shapes and full of enclosures. See also:

HYPERSTHENE

Hypersthene or See also:

BRONZITE

bronzite is less See also:

COMMON

common, but dark See also:

brown and green See also:

HORNBLENDE

hornblende are sometimes abundant. See also:

OLIVINE

Olivine also may be present; when the See also:

rock contains this in notable quantity it may be called an olivine monzonite. Numerous large prisms of See also:

APATITE

apatite often characterize micro-sections of monzonites, and See also:

ZIRCON

zircon, See also:

IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron ores and See also:

PYRITES

pyrites are frequent See also:

ACCESSORY

accessory minerals. rr The monzonites of Tirol show a See also:

GREAT

great variability in appearance, structure, and the relative proportions of their minerals. They tend to pass into rocks which have been called diabases and gabbros, and near the margins of the outcrop facies very See also:

rich in See also:

PYROXENE

pyroxene (pyroxenites) occur. Many authors believe that this variety of types is associated with the fact that the monzonites occupy a See also:

MIDDLE

middle See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place as regards their chemical See also:

composition between the See also:

ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid and the basic igneous rocks, and that such a magma is naturally somewhat unstable, and likely to split up or differentiate into partial magmas of more siliceous and less siliceous See also:

CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character.

The monzonites in fact approach rather closely to the calculated mean composition of the See also:

OUTER

outer portion of the See also:

earth's crust and from a molten magma of this nature it is natural to suppose that all kinds of igneous rocks have been derived. Rocks of monzonitic facies occur also in See also:

Norway, where they have been described as akerites. They contain quartz, orthoclase and plagioclase, augite and dark brown biotite; hornblende and hypersthene also may be present. Some of them have porphyritic rather than granitic texture, especially near the margins of the laccolites. From a study of these and other occurrences See also:

BROGGER, WALDEMAR CHRISTOFER (1851— )

Brogger proposed to define the monzonites as orthoclase-plagioclase rocks in which the two See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief classes of See also:

FELSPAR, or FELDSPAR

felspar occur in nearly equal quantities (as distinguished from the orthoclase rocks or granites and syenites and the plagioclase rocks or diorites and gabbros). At Yogo See also:

PEAK, THE

Peak and See also:

Beaver See also:

Creek in See also:

MONTANA

Montana, U.S.A., there are masses of granitoid rock which See also:

bear a See also:

close resemblance to the monzonites of Tirol. Two See also:

main types occur: (a) yogoite, which differs little from monzonite, and (b) shonkinite, which is a more basic rock richer in plagioclase and augite; this rock contains olivine and in places passes into dark pyroxenites. In shonkinite also a little See also:

NEPHELINE

nepheline may be present. In several places in the See also:

west of See also:

Scotland (See also:

ARGYLLSHIRE

Argyllshire) intrusive bosses are known which consist of an olivine-bearing rock closely related to monzonite. It has been called kentallenite because it is quarried at Kentallen in Argyllshire. Large crystals of pale green augite and irregular plates of biotite which enclose idiomorphic plagioclase felspar are conspicuous in micro-sections of this rock, and the abundance of olivine is rather greater than is usual in the monzonites; it is associated with diorites of lamprophyric character and dark pyroxenites and peridotites.

End of Article: MONZONITE

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