Calcite (or Dolomite) in a Marble
The views above show calcite (or dolomite) in a marble from the Adirondack Mountains, New York. The field of view is about 2 mm across. Minor graphite (opaque) is also present as long skinny flakes in the carbonate.
Most of this view is one large grain showing
two sets of twins. Calcite is invariably
twinned but the twins do not show
at all orientations. The largest grain is oriented so many of
the twin lamellae are at extinction
(black in XP). Very high order interference
colors -- high order pastels -- show along the (not extinct)
twin lamellae. The large grain to
the upper left is oriented such that twins
do not show. This grain has interference
colors that are of such high order that they appear white.
Epidote, Dolomite and minor Pholgopite in a Marble
This is a marble from Essex County, New Jersey. The twinned dolomite is clear (PP) and shows high order, almost white, interference colors (XP). Dolomite, like calcite, is one of the few minerals that shows twins in both PP and XP. Epidote, also present, has greater relief than the surrounding dolomite and has a very light pistachio green color (PP). The epidote shows a typical (for epidote) interference color pattern - blotchy high order colors of many hues. Several flakes of brown-green phlogopite (PP) can also be seen.
The field of view is about 2.5 mm across.