Geoscience Reference
In-Depth Information
Schist is a common metamorphic rock that exhibits
an alignment of platy and other elongated minerals
called schistosity. As schist will part relatively easily
along the plane of schistosity it is used locally for
building. Figure
79
shows a garnet-mica schist from
Norway. Gniess is a foliated rock with minerals aligned
alternately in fairly large-scale parallel layers known as
gneissose banding. This banding produces some
attractive stones. Figure
80
shows a charnokite gneiss
from India that is used for flooring and lining.
Metaquartzite is produced when a sandstone is
metamorphosed causing the constituents to recrystallize
into an interlocking mosaic of quartz. Figure
81
shows
'Alta Quartzite', a silver grey-green micaceous quartzite
from Norway that is used for flooring and paving. Figure
82
shows 'Azul de Macaubas', a decorative blue quartzite
from Brazil.
Marble is a prestigious stone formed by the
metamorphism of limestone. The limestone is
recrystallized to produce an interlocking granular mosaic
of roughly equal-sized calcite crystals. Pure marble is
made entirely of calcium carbonate and is white in colour
and thin slabs may appear translucent. Impurities in the
original limestone produce coloured marble (black, grey,
green, pink, red, yellow) that may have a mottled or
veined appearance. 'Statuario Venarto' is a Carrara
79
80
79
'Furuland Schist' (Norway) consisting of well
aligned crystals of quartz (grey/white), muscovite mica
(orange/pink), and garnet (black); XPT, ×35.
80
'Shivakashi' charnokite gneiss (India) with a
foliated texture, consisting of quartz (grey) and
feldspar (grey, twinned) with minor garnet (black) and
orthopyroxene (orange); XPT, ×35.
81
82
81
'Alta Quartzite' (Norway) consisting mainly of
quartz (grey) with minor proportions of feldspar and
muscovite mica (pink); XPT, ×25.
82
'Azul de Macaubas' (Brazil) consisting mainly of
quartz (grey) with minor proportions of the fibrous
mineral dumortierite (brightly coloured); XPT, ×35.
