Marble - Colorado Geological Survey

dote, is tightly cemented by silica, and is very
slightly calcareous. (Sample not digested.)
ATH-4 (43) Hornfelsic quartz sandstone
(quartzite) splotchy grayish orange 10 YR 7/4
to dark reddish brown 2.5 YR 3/6 where stained
by hematite. Rock is very fine grained and
shows no relict sedimentary structure nor is it
calcareous. (Sample not digested.)
AEQ-5 (44) Hornfelsic quartz sandstone
(quartzite) as AIII-4 (43).
ATV (45) Marble, medium dark gray N4,
medium grained with medium dark gray N4
calcite crystals 0.5 to 1.0 mm across. Crystals
are tightly interlocked but rock disaggregates
easily because of weathering. Impurities in calcite
crystals give them their color and are probably
clay and organic matter. Less than 0.5
percent of the rock is accessory pyrite which is
oxidized and stains the rock with staining halos.
There is some minor accessory quartz also.
ATV-1 (46) Marble, medium light gray N6,
medium grained with medium light gray closely
interlocked calcite crystals 0.5 to 1.0 mm
across. Rock has accessories of 0.1 percent oxidized
pyrite and magnetite which do not have
staining halos around individual crystals. Rock
is somewhat weathered but does not disaggregate
readily.
AIV-2 (47) Marble as ATV except sample is
more weathered.
AIV-3 (48) Marble, medium light gray N6,
medium grained with medium light gray closely
interlocked calcite crystals 0.5 mm to 1.0 mm
across. Rock has accessories of pyrite, magnetite,
and limonite after pyrite and magnetite in
less than 0.1 percent of the rock. Slight staining
in a few places is in evidence in the hand
specimen. Rock does not disaggregate readily.
ATV-4 (49) Marble, very light gray N8 to
light greenish gray 5 GY 8/1, medium grained
with calcite crystals ranging from 0.5 to 1.0
mm across. Calcite crystals are tightly interlocked
and show excellent resistance to disaggregation.
Rock contains less than 0.1 percent
pyrite and magnetite and there is slight pinpoint
staining in the vicinity of these crystals
where oxidized. Less than 0.1 percent of rock is
white muscovite mica. The slightly greenish
color of the hand specimen is caused by indistinct
zones of finely disseminated chlorite.
Staining on weathered surface is caused by
oxidation of iron minerals
ATV-5 (50) Hornfels (low grade contact
metamorphosed rock). Rock consists predominantly
of gypsum crystals elongate to as much
as 10 mm stained by hematite to 5 YR 5/8
yellowish red which make up ca. 80 percent of
the rock. Similarly stained quartz (10 percent),
5 percent of 2.5 YR 3/6 dark red hematite and
specular hematite, and probably other unidentified
accessory minerals including pyrite,
magnetite, moscovite-phlogopite, and possibly
barite make up the remainder of the sample.
(Sample not digested.)
AIV-6 (51) Quartzite Hornfels, medium
light gray N6 on fresh fracture and stained to a
mottled darker gray and red 2.5 YR 5/8 where
(apparently) stained by limonite. Some impurities
(undetermined) are present in the very
fine grained quartz. Sample not digested.
ATV-7 (52) Quartzite Hornfels, as ATV-7
(51) except it is darker medium dark gray N4
on fresh fracture. Sample shows some alteration
and solution(?) voids.
AIV-8 (53) Quartzite Hornfels as A-TV-7
(52).
ATV-9 (54) Quartzite Hornfels, mottled
red 2.5 YR 5/8 resulting from oxidation to limonite
of magnetite-?. Crystalline quartz is
vitreous and shows no relict sedimentary structure.
Where limonite staining is not apparent
the rock is a fine crystalline quartzite light
gray N7. (Sample not digested.)
ATV-10 (55) Quartzite Hornfels, as ATV-7
(52).
R-l (56) Quartzitic marble, medium light
gray N6, fine grained. Rock consists of a tight
fine grained "matrix" of crystalline quartz with
intergrain crystals of calcite and dolomite.
Finely disseminated pyrite and magnetite and
found throughout the sample and make up ca.
5 percent of the rock. Estimated percentages of
other minerals are 50 percent calcite 40 percent
quartz and 5 percent dolomite. Color of rock is
caused by relatively high percentage of dark
minerals.