The collection below includes both common and unusual rocks found in Vermont, three State Rocks ( granite, marble and slate), and talc, the State Mineral. Click on each sample for a larger image.
For a list of minerals reported in literature, click here.
Click here for Green Rocks in Vermont and check out the photogalleries and Earth Resources pages (left menu).
2. Fossilferous limestone
3. Muscovite schist
5. Monkton Quartzite
6. Shelburne Marble
11. Magnetite schist
12. Phyllite with pyrite
15. Cheshire Quartzite
17. Graphitic schist
19. Micaceous marble
Granite is a medium to coarse grained, light-colored,
intrusive igneous rocks that is composed of feldspar, quartz, and mica.
The feldspar, usually white or pink in color, is a potassium feldspar
(orthoclase and/or microline). Albite (Na rich plagioclase feldspar)
or oligoclase, a plagioclase feldspar with more sodium (Na) than calcium
(Ca), is commonly present in small amounts. Quartz is grey or glassy
in appearance. Small amounts of black mica (biotite) and/or white mica (muscovite) are present as platy
minerals. Hornblende needles (an amphibole), and rarely pyroxene, may
make up the mafic (dark-colored) parts of the rock. Accessory minerals
(less than 2% of the mineral content) may be present in the granite.
Zircon, a mineral that contains uranium, is normally present in granite
and is used by the geochronologist in Uranium/ Lead (U/Pb) analysis
to determine the age of crystallization for the rock.
Granite formed from the cooling of molten material
(magma) deep underground. The name "granite" is derived from
the fact that the rock appears to be composed of numerous "grains"
or crystals that are intergrown to
form a solid, durable rock.
Granite is a commercially valuable rock in Vermont. The granite
industry, centered in Barre, has been in operation since the 1800's.
Commercial uses of granite include monument stone, building stone, street
curbing, and crushed rock aggregate.
Granite, one of the State Rocks of Vermont, is abundant in the
northeastern section of Vermont. This sample was collected from the
Rock of Ages quarry in Barre. The granite is Devonian in age (around
380 million years old).
Fossiliferous limestone, South Hero, VT
This rock is a medium gray, fine- to medium- grained, limestone with fossil
fragments. The rock is mainly composed of calcite. Fossil fragments,
most less than 3mm across, are visible. The sample of fossiliferous
limestone was collected from a highway aggregate quarry on South Hero
Island. The rock is from the Ordovician ( 460 million years old) Glens
Most limestone develops as a result of the accumulation of the shells
or hard skeletal remains of marine organisms. As these accumulations
are buried and compacted by younger sedimentary deposits, the voids
are gradually filled by finer particles, some solution and recrystallization
occurs, and finally the entire mass hardens into a solid rock. Ancient
limestones, as represented by this sample, have been buried for millions
of years and the rock is very dense and hard.
Limestones of this type are often quarried and sold as "marble"
and when polished make remarkably beautiful building stone. The waste
rock can be crushed and used for highway aggregate and other commercial
products such as agricultural lime. There are numerous commercial limestone
quarries in western Vermont.
Muscovite schist with quartz and garnet, Chester, VT
This sample is a medium- grained muscovite schist composed
primarily of muscovite and quartz
with garnet porphyroblasts. The sample of the Gassetts Schist is from
the Cavendish Formation and is Cambrian in age. The sample was collected
near Gassetts (Chester, Vermont) on the west flank of the Chester dome.
In this sample, garnet is the dark red
mineral that appears as rounded eight-sided crystals. Muscovite is the
silvery white, flaky mineral that makes up the masses surrounding the
garnets. Quartz is the grey-colored mineral with the glassy appearance
that occurs in clusters, layers, or lenses.
The mineral content of a metamorphic rock such as schist is dependent
on both the chemical composition of the original rocks and the temperature
and pressure of the metamorphic environment. Different minerals (or
combinations of minerals) will crystallize under different temperature
and pressure conditions.
4. Kaolinite, Monkton, VT
Kaolin is composed almost exclusively of the clay mineral kaolinite,
a hydrous aluminum silicate [Al2(Si2O5)(OH)4]. Pure kaolin is solid
white in color and has a soft, silky feeling. The gritty feeling in
this sample is due to quartz impurities in the kaolinite.
"Kaolin rock" was mined sporadically at Monkton from the early
1800's until the late 1960's. The deposit was not pure and contained
quartz impurities. These impurities were costly to remove and were detrimental
to the products that were manufactured using kaolinite. Kaolinite was
used as fillers in paints and plastics and in the manufacture of glossy
paper. The cost and difficulty in removing the impurities lead to the
abandonment of the Monkton site.
Kaolinite was also mined in Bennington and Shaftsbury in the
late 1800's and early 1900's. This clay was used in the early pottery
industry of that area.
Kaolinite deposits are rare in Vermont. Their occurrence at the base
of the Cambrian Cheshire Quartzite is unique and
restricts their location to a linear, north-south belt along
the western side of the State where the Cheshire Formation is present.
The Cheshire Formation is approximately 570 million years old.
Monkton Quartzite, Winooski, VT
The sample is a reddish- buff quartzite composed of round to angular
quartz sand grains cemented by quartz (SiO2) with some iron oxide (FeO2,
producing the red color) and calcite (CaCO3). This rock is a sedimentary
orthoquartzite that has not been subjected to sufficient heat and pressure
to recrystallize the rock. Cementation and compaction have created a
very durable rock
This orthoquartzite is from the Cambrian Monkton Formation and
was collected near Winooski. Quarries near Burlington supplied blocks
of Monkton Quartzite used to build the Redstone Campus at the University
6. Marble, Danby, VT
This rock is a white, massive, medium-grained marble composed
principally of calcite. Some green or dark streaks are due to the presence
of pyrite, chalcopyrite, muscovite, or chlorite.
This sample was collected from the OMYA, Inc. quarry in Danby.
The rock belongs to the Columbian Marble Member of the Shelburne Formation
(Lower Ordovician age).
Marble, a metamorphic rock composed principally of calcite, is found
in western Vermont. The marble in Vermont was formed by the
metamorphism of Cambrian
to Ordovician age limestones. Marble from Vermont's Danby quarry has
been used in famous buildings such as the Thomas Jefferson Memorial in Washington,
D.C., the United Nations Building in New York, and the Chiang Kai-Shek
Memorial in Taiwan. Most marble currently quarried in the state is crushed
and used as filler in paint, paper
Marble is an important natural resource and has been a long-standing
industry in Vermont. Marble is one of the State Rocks of Vermont.
Greenstone, Middlesex, VT
The rock is a dark green, fine-to-medium-grained, massive greenstone
(mafic schist) composed of chlorite, albite, epidote, actinolite, quartz
and calcite. This greenstone, from the Cambrian/Ordovician Stowe Formation, may
also have distinct light-colored compositional layers of albite, quartz
Greenstones are common in many Vermont rock formations. They are metamorphosed
volcanically derived sediments, igneous
lava flows, pillow lavas or dikes that were originally of basaltic composition.
They are interlayered with metamorphosed sedimentary rocks. Detailed
chemical information on the Vermont greenstones has helped to reveal
the nature of the environment (island arc, mid-ocean ridge, rift, etc)
where the greenstones and associated rocks were originally formed.
Gneiss, Chester, VT
Gneiss (pronounced "nice") is
a metamorphic rock. Some of the oldest rocks on Earth are gneiss.
The foliation, or layering, in gneiss has distinguishing characteristics
that set it apart from other metamorphic rocks. Layers or lenses (lenticules)
of granular (rounded) minerals alternate with layers of flaky or elongated
minerals. The granular minerals are usually the light-colored calcium,
sodium, and potassium rich minerals such as quartz and the various types
of feldspar. The alternating layers are commonly composed of dark-colored
iron and magnesium rich minerals including biotite, chlorite, and hornblende.
Since the mineralogy of many gneisses (quartz, feldspar, and mica) is
similar to that of granite (see #1), many gneisses are referred to as
granite gneiss. A granite gneiss may be derived from the metamorphism
of a granite (an igneous rock) or may simply be a product of the metamorphism
of a sedimentary rock that happens to have a composition similar to
Gneiss is an abundant rock type
in the Precambrian age "core" of the Green Mountains and areas
of the southern Green Mountains. Areas
where Precambrian rock (older than 570 million years before the present)
is exposed are known as massifs. This sample was collected from an area
of Precambrian rock located north of Chester. The gneiss exposures in
this area are part of the Precambrian-age Mount Holly Complex.
Amphibolite, Sharon, VT
This dark gray to black, medium- grained amphibolite consists
of amphibole and plagioclase with little or no quartz. Hornblende is
perhaps the most common mineral in the amphibole group; actinolite is
also present in many amphibolites. The name amphibolite is given to
this rock type because of the abundant and remarkably prominent crystals
of hornblende (black needles).
The amphibolite in this collection has been interpreted as the metamorphic
equivalent of an igneous basalt. This rock is believed to have originated
as a basaltic lava flow during the Late Silurian-Early Devonian Period
some 400 million years ago.
This rock was collected in Dummerston Center from the Standing Pond
Volcanics. The type locality for the rock is at Standing Pond in Sharon.
Black Shale, South Hero, VT
Shale is a very fine-textured sedimentary
rock that is relatively dense. Shale is composed of very fine(clay and
silt size) particles. The particles are minerals that were weathered and
eroded from rocks in a source area that was at some distance from the
area where the sediment was finally deposited. Shales represent deposition
in a quiet environment.
Although shale may occur in a variety of colors, shale
in Vermont is usually dark grey or black. Where it occurs as thinly
laminated strata, shale is often mistaken for slate (a
metamorphic relative described below).
This black shale is both carbonaceous
(contains carbon, C) and calcareous (contains calcium carbonate,
CaCO3). Shales of this type may be found at many locations in the Champlain
Valley, especially on the shores of Lake Champlain and throughout the
Champlain Islands. This sample was collected from a quarry on South Hero
Island. It is from the Ordovician Stony Point Formation (around 460 million
11. Magnetite schist, Jonesville, VT
In this schist, the mineral magnetite occurs
as black "knots" or porphyroblasts in a finer-grained matrix
composed of muscovite, chlorite, quartz, and albite. Small grains of pyrite
and garnet are present in some samples. The magnetite is strongly magnetic
and will be attracted by a small hand magnet. A small magnet suspended
on a string will be pulled slightly toward a porphyroblast of magnetite.
Magnetite schists are not rare in Vermont. This rock and other magnetite-bearing
rocks are unique, however, because the presence of this mineral in a rock
will cause a compass needle to deviate from a normal magnetic north direction.
Woodsmen, hikers, and others who depend on a compass to find their way
may become disoriented where this rock is present.
The sample was collected near Jonesville, Vermont from the Underhill Formation
(around 550 million years old).
Phyllite with pyrite, Montpelier, VT
This sample is a very fine-grained, black
to dark gray, quartz-sericite phyllite with pyrite. The phyllite is
a metamorphic rock that formed at thermodynamic (temperature and pressure)
conditions intermediate between those that produce slate (low temperature,
high pressure) and those that produce schist (higher temperature, higher
pressure). Phyllite is a fine-grained, foliated (layered) rock like
slate but additionally shows a "crinkly" or "wavy"
character along the rock cleavage surfaces.
Large crystals of the bronze-yellow colored mineral pyrite are present
in this sample. Pyrite (FeS2) is composed of both iron and sulphur.
Its bronze-yellow color often causes pyrite to be mistaken for gold,
and a common name for pyrite is "fool's gold".
Phyllite may be found in the eastern part of the Green Mountains and
in areas of the Vermont Piedmont. This sample of phyllite with pyrite
was collected near Montpelier from the Silurian-Devonian Waits River
Formation (around 415-390 million years old).
13. Concretion, VT
The term concretion is a general
term used for peculiar mineral segregations found in sedimentary deposits.
In Vermont, concretions are found in the fine-grained silt and the very
fine-grained sand layers associated with glacial lake sediments. These
very fine-grained layers are commonly called varved clays.
Concretions are composed of concentrations of common sediment and cementing
materials such as calcium carbonate (CaCO3) and/or iron oxide (FeO2).
The cementing material fills in the pore space around the fine sediment
grains and binds the sediment to form a variety of shapes. Often, the
cement crystallizes around a central nucleus and forms concentrically
banded, oval-shaped nodules. Concretions are most often restricted to
one narrow bed or layer and thus tend to be quite flat.
Button Bay, on the east shore of Lake Champlain, was originally named
"Button Mould Bay" for the numerous concretions that were
found washed out of glacial lake clay beds now exposed along the Lake
Champlain shoreline. The concretions reminded the early inhabitants
of the molds used in the making of pewter buttons.
The concretion sample in this collection was collected from Pleistocene
age (15,000 to 10,000 years old) glacial lake sediments in either East
Montpelier or Putney.
14. Talc and soapstone, Windham, VT
Talc, our State Mineral, is very soft and is used in talcum powder.
Talc is a hydrous magnesium silicate, Mg6Si8O20(OH)4, and is formed
during the metamorphism of ultramafic rocks such as serpentinite. The
metamorphism occurs in the presence of hot fluids circulating through
the rocks (hydrothermal alteration).
The Green Mountains are comprised of
folded and faulted metasedimentary rocks, metamorphosed volcanic
rocks and slivers of ocean crust (serpentinized ultramafic rocks). Talc,
soapstone, verde antique and asbestos are usually associated with the
ultramafic rocks. The bodies of serpentinite occur almost exclusively
within two rock formations, the Ottauquechee and Stowe Formations (Cambrian-Ordovician
in age, between 550 and 500 million years old). The isolated occurrences
of talc extend the full length of the state.
Talc is an economically valuable mineral used in cosmetics, in the manufacture
of paper, paint, and insecticides, in ceramics, and by the roofing materials
and tire industries. It is also used to coat products which need to
slide apart easily, such as nested stacks of plastic pails in a hardware
store. Soapstone, composed of chlorite and talc, can withstand intense
heat and is used by some Vermont companies to make woodstoves, countertops
The sample was collected from a talc mine in Windham.
15. Quartzite, Danby, VT
is a word used interchangeably for both metamorphic quartzites (known
as metaquartzite) and sedimentary quartzite (known as orthoquartzite).
This sample of metaquartzite is a greyish-white
rock composed almost exclusively of intergrown quartz crystals. The
rock was formed during regional metamorphism by complete recrystallization
of a pure, quartz sandstone. Pure, white metaquartzite is
present along the western edge of the Green Mountains. This rock type
forms the "Green Mountain Front" in southern Vermont. This
sample is from the Cheshire Formation of Cambrian age (around 540 million
years old) and was collected near Danby from Big Brook.
Dolostone, Ludlow and Milton, VT
These pinkish-white and buff, mottled
dolostones are slightly metamorphosed
rocks that were not greatly altered from an original sedimentary state. Dolostone is the name of a sedimentary rock
that is dominantly composed of the mineral dolomite (CaMg(CO3)2). Dolomite is a carbonate mineral similar to
calcite (CaCO3), the dominant mineral in limestone and marble. Dolostones
are easily distinguished from limestones by using the dilute hydrochloric
acid (HCL) test. The reaction of a drop of this solution on the rock
specimen will determine the presence of calcite (CaCO3) or dolomite
[CaMg(CO3)2]. Limestone (CaCO3) effervesces easily and vigorously, but
the same reaction occurs very sluggishly on dolostone. The presence
of some magnesium (Mg), in place of some of the calcium (Ca), in the
mineral dolomite means that the reaction of the acid is slower.
Dolostones are common in western Vermont in the Champlain Valley and
the Vermont Valley ( a narrow valley located between the Taconic Mountains
and the Green Mountains). Dolostones are less common in the Green Mountains
and the Vermont Piedmont in central and eastern Vermont.
The mottled dolostone is the Dunham Dolomite which represents the initial
deposition of carbonates on the shelf margin of Iapetus during Cambrian
The plain buff-colored dolostone is from the Tyson Formation in Ludlow,
VT. It is also Cambrian in age
(550 million years old)
17. Graphitic, black schist, Morrisville, VT
is a fine-grained, black, graphitic, quartz-albite-sericite schist with
pyrite. If you rub your fingers over the surface of this rock, the rock
will feel greasy and your fingers
will be blackened with a fine black film of graphite. Graphite has a
structure similar to mica (flaky) and a hardness similar to talc (very
The graphitic schist was originally formed
as a sedimentary rock that was rich in carbon (C). During metamorphism,
the rock was recrystallized in an oxygen-starved environment and a rock
made of carbon (seen as the mineral graphite) and iron sulfide (FeS,
or pyrite) was produced.
This sample was collected near Morrisville from the Ottauquechee Formation
(around 525 million years old).
18. Serpentinite, Rochester, VT
is a dark green-colored rock that is composed of serpentine, a hydrous
magnesium silicate mineral, (Mg, Fe)3Si2O5(OH)4. The rock is usually
crisscrossed with white veins of calcite (calcium carbonate, CaCO3)
and/or magnesite (magnesium carbonate, MgCO3). Serpentinite acquires
a brilliant and durable surface when polished, and is a popular dimension
stone used as building facings or decorative interior walls. Verde antique
is the commercial name for polished serpentinite.
Serpentinite is commonly found as isolated, ultramafic (high amounts
of mafic minerals containing iron and magnesium) bodies in Vermont and
occurs primarily within a narrow zone in the Green Mountains that stretches
from Massachusetts to Canada. Serpentinite was produced through alteration
of peridotite or dunite, ultramafic igneous rocks. Serpentinite in Vermont
is believed to be remnants of oceanic crust that were incorporated with
ocean sediments as continents collided and the Green Mountains were
formed during the Taconic and Acadian Orogenies.
The sample of serpentinite in this collection was quarried in Rochester,
Micaceous Marble (Crystalline Limestone), Berlin,
Micaceous marble (crystalline
limestone) is a metamorphic rock that was derived from
calcareous mudstones and shales. The marble is termed "impure"
because of the abundance of material that is not pure calcium carbonate
Impure marble is common in the Waits River Formation which dominates
geology of the eastern half of Vermont (the Vermont Piedmont). The impure
marble beds and lenses are interbedded with schist, phyllite, and impure
quartzite. In exposed outcrops, the weathered, impure marble has a light
to dark brown color. With progressive leaching of the calcium carbonate
(CaCO3), a rusty brown colored, porous, permeable, crumbly crust develops.
This crust is composed of a spongy mass of iron oxide-stained mica grains.
The beds with this type of weathering pattern are often referred to
as the "punky brown beds" of the Waits River Formation.
The Waits River Formation probably formed in a moderately deep, marine
as turbidite deposits or soft sediment slump deposits of calcareous
shales, mudstones, and muddy sandstones. Fossils found in this formation
indicate the rock is approximately 400-425 million years old, placing
it in the Late Silurian-Early Devonian time period.
This sample of micaceous marble was collected in Berlin from the Waits
20. Slate, Southwestern VT
These samples are very fine-grained, medium
gray-green, green-purple mottled, and purple slates. Slate is composed
mainly of quartz, feldspar, carbonates, chlorite and micas. Slate may
be found in a variety of colors. The green slate contains chlorite.
Colors are imparted to the rock by very minor amounts of iron oxide
(red), carbon (black), and other pigments or mineral constituents. The
most common colors are black, grey, green, purple, and red. Vermont
is somewhat unique in the production of green and purple slates.
Slate, one of the State Rocks of Vermont,
is a metamorphic rock that is a product of recrystallization
of shale or other fine-grained sedimentary rocks under conditions of
low temperature and high pressure. The new minerals that are produced
are primarily platy varieties, such as mica and chlorite, and are microscopic
Slate may be distinguished from shale (its sedimentary counterpart)
in a number of ways. Slate has a higher luster, is somewhat harder and
denser, and splits more evenly along parallel foliation surfaces.
The minerals in slate crystallize with their flat, plate-like dimension
aligned at right angles to the direction of applied pressure. This alignment
of minerals produces a unique structure called "slaty cleavage".
Slaty cleavage may be parallel to the original layering or, as is most
often the case, at a high angle to the original bedding or lamination
surfaces. This can result in outcrops where the bedding (defined by
compositional differences in the layers) is nearly horizontal in orientation
and the cleavage is nearly vertical.
The rock is quarried for commercial
purposes. Vermont has had a slate industry since the mid -1800's. Today,
the slate industry is located in the southwestern part of Vermont around
Poultney, Pawlet, and Fair Haven. Commercial uses for slate include
roofing slate, flooring tile, and flagstones. Some older school blackboards
were made from slate.
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