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ROCK FORMATIONS

FIG.

I

FIG. 2

Micro-photograph of thin section of granite, from Lokken, Norway, between crossed nichols, showing patchy appearance of soda-orthoclase (O), irregular plates of quartz (Q), and illustrating granitoid (xenomorphic or allotrimorphic) texture. The orthoclase shows twinning.

Micro-photograph of thin section of augite-syenite from Laurvik, Norway, between crossed nichols. The photograph shows only plain non-striated orthoclase and illustrates granitoid allotrimorphic or xenomorphic texture. The lines due to cleavage.

FIG. 3 Micro-photograph of thin section of norite, from Hitteroe, Norway,
between crossed nichols, showing banded plagioclase Labradorite
(PI), an opaque ore, ilmenite (I), and a monoclinic pyroxene diallage
(D). The section also illustrates granitoid (xenomorphic or allo-
trimorphic) texture. A fringe of biotite surrounds part of the ore.
FIG. 4 Micro-photograph of thin section of Perthite, between crossed nichols,
showing intergrowth of albite (Ab) and microcline (Mi). · The albite
shows banding and the microcline cross-hatching.

FIG. 5 Micro-photograph of thin section of graphic granite from New Bedford,
Mass., between crossed nichols, showing parallel intergrowth of
quartz (Q) and microcline (Mi). The latter shows cross-hatching.
FIG. 6 Micro-photograph of thin section of porphyritic perlite showing sanidin
crystals (S) in glassy ground mass. Dark wavy bands indicate flow
in the mass before cooling (flow structure).
Thin section of porphyritic trachite showing sanidin (S) and biotite
(B) in glassy ground mass. The crystals have been co-eroded or
redissolved by the magma as is shown by their even curved
boundaries.

FIG. 7

FIG. 8 Micro-photograph of thin section of tinguaite porphyry from the
Odenwald showing idiomorphic crystals of nepheline (N), also an

indistinct zonal structure in the same.

FIG. 9 Micro-photograph of thin section of olivine norite, from Risor, Norway, showing long lath-shaped crystals of plagioclase (Pl), augite with characteristic nearly rectangular cleavage (A), olivine altered on the margins to serpentine (O1), and an opaque ore (M).. Micro-photograph of thin section of diabase between crossed nichols, showing ophitic structure. It contains plagioclase (P1), augite (A), and magnetite (M).

FIG. 10

FIG IT

Micro-photograph of thin section of Essexite from Gran, Norway, showing hypidiomorphic augite crystals (A), and opaque grains of magnetite (M) in a fine ground mass of plagioclase. It illustrates hypidiomorphic-porphyritic texture.

FIG. 12 Porphyritic basalt (meiaphyre) with phenocrysts of plagioclase (PI) in a dense micro-crystalline ground mass consisting of augite, magnetite and a second generation of plagioclase crystals.

ROCKS