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J. SCHETELIG
The faces (010), (110) and "(110) are bright and reflecting, the other
are dull, and show generally striation, as mentioned above probably due
corrosion.
The crystals are always twinned according to the albite*law indicated
by fine striation // a on (001). Twins according to the Carlsbad*law are
common. Striation on (010) according
to the pericline*law is very rarely
observed, and only partially developed
on well terminated areas of the cry*
stals. The angles between the pericline
lamellae and the trace of (001) on
(010) is about + 20°.
Aventurization and 1 a b r a*
dorization («Glaukosiren»).1 The
albite is developed as aventurine
feldspar («sunstone») and shows aven*
turization on (010) and (001). Ac*
cording to the results of the care*
ful investigation of aventurine feldspar
by Mr. Olaf Andersen2 the majo*
rity of the minute and thin lamellæ of haematite, producing the aventurisa*
tion, is in all cases chiefly arranged // the simple crystallographic planes
(150), (150), (112) and (112), a minor portion of the scales // other
planes as (001), (010), (113) and (021). The aventurization on (010) is
chiefly produced by lamellae // (150) and 150), and on (001) by lamellae
(112) and (ll2).
In our case, concerning the albite from Skarvebergbugten, it
seems evident that the majority of the lamellae of haematite shows arrange*
ment // (150) and (150) and also // (112) and (ll2). The distribution
of the lamellae is rather irregular, some crystals show innumerable re*
fleeting scales of haematite, other only a slight number. According to
examination under the microscope of orientated thin sections — mentioned
later on — numerous scales of haematite are observed in sections cut near
the surface of the crystals, but very few are shown in sections from the
inner part of large crystals.
In sections // (001) the major portion of scales of haematite // (112)
and (112) shows parallelogrammic outlines. Scales // (150) and (150)
1 C. Viola. Z. Kr. XXXIV. 171. 1901.
2 Olaf Andersen. On Aventurine Feldspar. Am. Journ. Sc. V. XL. oct. 1915.
124
Fig. 8. Crystal of Albite.
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