Marble - Colorado Geological Survey

(67) Quartzite, dark greenish gray 5 G 4/1,
fine grained with stringers of light greenish
gray 5 G 8/1 fine crystalline quartz. Rock is
apparently nearly pure quartz and possibly
owes it greenish color to minor finely
disseminated chlorite; chlorite crystals were
not seen. Limonite stains are present on one
edge of sample. (Sample not digested.)
(68) Marble, dark gray N3, fine crystalline
with tightly interlocked calcite crystals from
0.1 to 0.5 mm across. Crystals are same color
as hand specimen owing to presence of ca. 1-2
percent organic impurities and very minor less
than 0.1 percent magnetite contained within
the crystals. Rock shows excellent resistance to
disaggregation and on weathered surface shows
little staining.
(69) Marble, medium gray N5 with bands
ranging up to very light gray N8, coarse crystalline
with crystals ranging from 1.0-4.0 mm
across. Calcite crystals are tightly interlocked.
Lighter bands contain 1 to 2 percent slightly
oxidized magnetite and very minor less than
0.1 percent pyrite. Darker N5 areas contain
very minor ca. 0.1 percent iron minerals. Crystal
color is same as hand specimen owing to
less than 1 percent organic impurities contained
within crystals. Rock shows good resistance
to disaggregation on fresh surfaces and poor
resistance where weathered.
(70) Marble as (69) except larger crystals
range upwards to 6 mm across and the magne
tite is oxidized to hematite/limonite resulting
on a 2.5 YR 4/8 red splotchy staining in the
otherwise near white bands.
71) Marble, medium gray N5 coarse crystalline
with calcite crystals from 1.0 to 2.0 mm
across with calcite crystals tightly interlocked.
Calcite crystals are the same color as hand
specimen owing to organic impurities and clay
making up less than 1.0 percent of them. Very
minor less than 0.1 percent magnetite and
pyrite. An unidentified dark yellowish orange
10 YR 6/6 mineral, possibly sphene, forms less
than 0.1 percent of the rock. Stubby, prismatic
crystals 0.2-0.5 mm across do not disaggregate
or oxidize to stain or deteriorate adjacent calcite
crystals. Rock exhibits good resistance to
disaggregation except on weathered surface(s).
(72) Metaquartzite, hydrothermal ironsulfide
mineralized. Protolith of rock probably
is a quartz sandstone with a small amount of
clay or a quartz porphyry intrusive. Rock consists
of veinlets of finely disseminated crystalline
pyrite and minor magnetite? in a matrix y
N9 near white five grained crystalline quartz.
Biotite and phlogopite ? are distributed in
small 0.5 mm masses throughout the rock.
Estimated percentages of minerals are quartz
75 percent pyrite 15 percent, biotite/phlogopite
? 9+ percent, other undetermined constituents
1 percent. Note: There is a very small amount
0.1 percent of a soft jade-green mineral that
was not determined.