The 20 Rocks of Vermont
1. Granite, Barre, VT Granite is a medium to coarse grained, light-colored, intrusive
igneous rock that is composed of feldspar, quartz, and mica.
a. The feldspar, usually white or pink in color, is a potassium feldspar (orthoclase and/or microline).
b. Albite (Na rich plagioclase feldspar) or oligoclase, a plagioclase feldspar with more sodium (Na)
than calcium (Ca), is commonly present in small amounts.
c. Quartz is grey or glassy in appearance.
d. Small amounts of black mica (biotite) and/or white mica (muscovite) are present as platy minerals.
e. Hornblende needles (an amphibole), and rarely pyroxene, may make up the mafic (dark-colored)
parts of the rock.
f. Accessory minerals (less than 2% of the mineral content) may be present in the granite.
g. 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.
h. Granite is formed from the cooling of molten material (magma) deep underground.
i. 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.
j. 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.
k. 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).
2. Fossiliferous limestone, South Hero, VT This rock is a medium gray,
a.
b.
c.
d.
e.
f.
g.
h.
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 Falls Formation.
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.
3. 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.
a. The sample of the Gassetts Schist is from the Cavendish Formation and is Cambrian in age.
Muscovite schist with quartz and garnet, Chester, VT continued
b. The sample was collected near Gassetts (Chester, Vermont) on the west flank of the Chester
dome.
c. In this sample, garnet is the dark red mineral that appears as rounded eight-sided crystals.
d. Muscovite is the silvery white, flaky mineral that makes up the masses surrounding the garnets.
e. Quartz is the grey-colored mineral with the glassy appearance that occurs in clusters, layers, or
lenses.
f. 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.
g. 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].
a. 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.
b. "Kaolin rock" was mined sporadically at Monkton from the early 1800's until the late 1960's.
c. 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.
d. Kaolinite was used as fillers in paints and plastics and in the manufacture of glossy paper.
e. The cost and difficulty in removing the impurities lead to the abandonment of the Monkton site.
f. 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.
g. Kaolinite deposits are rare in Vermont.
h. 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.
i. The Cheshire Formation is approximately 570 million years old.
5. Monkton Quartzite, Winooski, VTThe sample is a reddish- buff quartzite composed
a.
b.
c.
d.
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 of Vermont.
6. Marble, Danby, VT This rock is a white, massive, medium-grained marble composed
a.
b.
c.
d.
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, Danby, VT continued
e. 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.
f. Most marble currently quarried in the state is crushed and used as filler in paint, paper and plastic.
g. Marble is an important natural resource and has been a long-standing industry in Vermont.
h. Marble is one of the State Rocks of Vermont.
7. Greenstone, Middlesex, VT The rock is a dark green, fine-to-medium-grained,
a.
b.
c.
d.
e.
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 lightcolored compositional layers of albite, quartz and epidote.
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.
8. Gneiss, Chester, VT Gneiss (pronounced "nice") is a metamorphic rock.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
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 granite.
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.
9. Amphibolite, Sharon, VT This dark gray to black, medium- grained amphibolite
a.
b.
c.
d.
e.
f.
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.
10. Black Shale, South Hero, VT Shale is a very fine-textured sedimentary rock that is
a.
b.
c.
d.
e.
f.
g.
h.
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 years old).
11. Magnetite schist, Jonesville, VT In this schist, the mineral magnetite occurs as
a.
b.
c.
d.
e.
f.
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. 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 (~ 550 million
years old).
12. Phyllite with pyrite, Montpelier, VT This sample is a very fine-grained, black to
a.
b.
c.
d.
e.
f.
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
a.
b.
c.
d.
e.
f.
g.
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 made 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 (15-10,000 years old)
glacial lake sediments in either East Montpelier or Putney.
14. Talc and soapstone, Windham, VT Talc, our State Mineral,
a.
b.
c.
d.
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 and soapstone, Windham, VT continued
e.
f.
g.
h.
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 and sinks.
The sample was collected from a talc mine in Windham.
15. Quartzite, Danby, VT "Quartzite" is a word used interchangeably for both metamorphic
a.
b.
c.
d.
e.
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 Mtns.
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.
16. Dolostone, Ludlow and Milton, VT These pinkish-white and buff, mottled
a.
b.
c.
d.
e.
f.
g.
h.
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 time.
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, VTThis is a fine-grained, black, graphitic,
a.
b.
c.
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 soft).
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 (~ 525 million years
old).
18. Serpentinite, Rochester, VT Serpentinite is a dark green-colored rock that is
a.
b.
c.
d.
e.
f.
g.
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, CaCO 3) 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 Vt is believed to be remnants of oceanic crust that were incorporated with ocean
sediments as continents collided and the Green Mtns were formed during the Taconic &
Acadian Orogenies.
The sample of serpentinite in this collection was quarried in Rochester, Vermont.
19. Micaceous Marble (Crystalline Limestone), Berlin, VT Micaceous marble
a.
b.
c.
d.
e.
f.
g.
h.
(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 CaCO3.
Impure marble is common in the Waits River Formation which dominates the bedrock 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 oxidestained 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 environment 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 River Formation.
20. Slate, Southwestern VT These samples are very fine-grained, medium gray-green,
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
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 size.
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 ( Poultney, Pawlet, & Fair
Haven).
Commercial uses for slate include roofing slate, flooring tile, and flagstones. Some older school
blackboards were made from slate.