The Minerals

by David E. Jensen

The minerals that can be found in the Genesee country are those that are present in the sedimentary rocks or occur in the rocks of the glacial drift. Sedimentary rocks do not have an abundance of mineral species, yet some of the minerals that can be found in the region rank among the finest examples of their kind in the world.

Mineral Occurrences in the Sedimentary Rocks

The Lockport dolomite
The Lockport dolomite is well known to mineral collectors for the variety and beauty of the mineral species that may be found in irregular cavities in the rock. One of the earliest references on mineral localities, A Catalogue of American Minerals with Their Localities, by Samuel Robinson, MD, in 1825, lists three species each from Brighten and Rochester and 12 species from Lockport, all from this rock layer.

This gray massive rock is named from its occurrence at Lockport, New York. It extends westward through Ontario, Canada, into Michigan and eastward into Wayne County, New York. It is quite resistant to erosion and it forms the crests of Niagara Falls and the Upper Falls of the Genesee River in Rochester. It is also responsible for the prominent ridge (escarpment) that lies south of Ridge Road in western New York and continues westward into Canada.

After the Barge Canal was built, the piles of Lockport dolomite along the canal west of Lockport and southwest of Rochester were an excellent source of minerals. In recent years, the rock has been crushed and widely used for highway construction. Numerous quarries have been opened in the vicinity of Rochester, west of Lockport and near Hamilton, Ontario. At times, these quarries expose sections of the rock formation that have an abundance of minerals. The minerals that can be found in the Lockport dolomite include:

The Furnaceville hematite Water-filled trenches with adjacent piles of rock and dirt north of Ontario Center in Wayne County are remnants of a mining industry that once flourished in the area. Indians were the first to discover that the red hematite rock was an excellent pigment. As early as 1797, the hematite was mined in Oneida County and later a small quantity of the ore was shipped from Wayne County during the War of 1812. The discoveries of larger and more profitable iron ores in the Adirondacks and elsewhere, together with the economic limitations of mining a thin iron ore layer, brought an end to the local iron ore industry, though for many years small quantities of the hematite were mined and used as a pigment in red barn paint.

The Furnaceville hematite is a hematite-bearing limestone that contains many fossils. It can be seen as a prominent red layer about 12 inches thick in the Genesee Gorge north of Driving Park Bridge. It also occurs in Densmore Creek.

The Onondaga limestone
This is an extensive limestone formation that outcrops and is quarried at many places from Buffalo eastward across the state to Jamesville and beyond. It contains an abundance of chert nodules. Chert is a hard mineral, a variety of quartz, and is sometimes called "flint" in the literature. The Indians once quarried the chert and fashioned it into arrowheads and scraping tools. In the Genesee country, quarries in the Le Roy area have an abundance of the cherty limestone. The soil and glacial drift in the southern part of the Genesee country contain nodules and pebbles of the chert from which much of the limestone has been eroded away.

Minerals in concretions and septaria
The shales of the Naples Group of rocks (late Devonian in age) contain occasional rounded to elongated dark gray nodules of limestone that range in size to over a foot in diameter. These nodules are called concretions. If they have one or several polygonal cracks that are filled with crystalline mineral material, they are called septaria. Often, in weathering, the septaria will develop a curious pattern that has led them to be erroneously identified as "petrified turtles". The minerals in the cracks are commonly calcite and pyrite with occasional ankerite, galena, limonite, selenite and sphalerite.

The hills near Bristol Center, Bare Hill in Yates County, and the shores of Canandaigua Lake north of Vine Valley and Seneca Point are places where concretions and septaria may be found.

Pyrite in the Hamilton shales
The shales of the Hamilton group are of mineralogical interest because some of the layers contain fossils that have been replaced by pyrite. Recent investigations show that pyrite is the mineral replacing the fossils, not marcasite as had previously been believed. (Ref.--Izard, J. E. and Clemency, C. V.)

At Spring Creek, Alden, near Buffalo, New York, the gray shales contain numerous nodules of partly crystallized pyrite that frequently contain fossils which have been replaced by pyrite. These magnificent specimens are highly prized by both mineral and fossil collectors. Near Leicester in Livingston County, a layer of pyritiferous limestone about 5 inches thick occurs at the base of the black Geneseo shale. This pyrite tends to disintegrate upon exposure to the atmosphere.

Minerals in the Rocks of the Glacial Drift

The term "glacial drift" refers to the assorted rock debris that was carried by the glacier from the source and deposited as the glacial ice melted. This rock debris includes the gravel, cobbles and boulders that occur in the soil, that are exposed in gravel pits, and some of the rock material that may be found on lake beaches and in streams and rivers of the Genesee country. Some of the rock material in the latter areas are the results of weathering of the local rocks.

Most of the rock materials transported by the glacier came from Canada, though some are from northern New York. These rocks include igneous rocks (granites, pegmatites, syenites, gabbros and anorthosites) and metamorphic rocks (quartzite, gneisses of many kinds and schists).

Since these rocks are usually abraded (rounded and roughened) by water or glacial action, it is not always easy to recognize the minerals that are present. Wetting the rocks with water or chipping off a small piece to reveal a fresh surface will aid the mineral identification. The commonest minerals are:

Quartz. This is usually milky white though sometimes partly transparent. It may be stained brown by soil or limonite and red by iron oxide. It is present in granites, pegmatites, gneisses and quartzites. It is also the main constituent of the local sandstones.

Feldspar. This mineral has a good cleavage which can be observed on a freshly broken surface. The flesh colored feldspars are microcline which is sometimes intergrown with albite (perthite). The white and light gray feldspars are usually andesine-oligoclase and the dark gray feldspars are labradorite.

Hornblende. This is a dark green to black mineral with typical amphibole cleavage. It is found in granites, syenites and gneisses.

Pyroxene. A dark green pyroxene, augite, is a constituent of gabbros, some syenites and gneisses.

Aegirite may also occur but is difficult to recognize without the aid of a microscope.

Hypersthene is a bronze-black to black orthorhombic pyroxene that usually has a metallic pearly luster on a cleavage surface. It occurs in gabbros.

Epidote. This is a pistachio green mineral that is found in gneiss, sometimes with pink feldspar and quartz.

Chlorite. This is a gray-green to green mineral that occurs in some gneisses and schists.

Garnet. This red to brownish red mineral is found in gneisses, sometimes in round grains and crude crystals that may be 1/4 inch and more in diameter.

Magnetite. This black metallic mineral can be recognized by its attraction to a magnet. It is found in granites and gneisses.

Serpentine. This is a dark green mineral that occurs in serpentinites.

The amateur gem cutter may find that many of the glacial rocks can be cut and polished to make unusual gems or decorative pieces.

The Minerals in Lake Ontario Sands

The sands of Lake Ontario beaches contain many interesting minerals, some of which can be recognized without the aid of a microscope. A small magnet will attract grains of black magnetite. A black, non-magnetic mineral is hornblende. Red translucent grains of garnet are quite abundant. Quartz is present, usually as milky white grains, sometimes partly clear and sometimes stained by soil or iron oxide.

Altogether, over 25 minerals have been reported from Lake Ontario beach sands but their identification requires the use of a petrographic microscope. Among the most common of these not mentioned above are: augite, corundum, epidote, hypersthene, rutile, sillimanite, sphene (titanite) and zircon.

Descriptions of the Minerals

The following list of minerals is arranged according to their chemical composition as established by the Dana's System of Mineralogy, 7th Edition. Descriptions of physical properties of the minerals have been omitted. This information can be obtained by reference to any of several excellent textbooks on minerals.

The list of minerals includes the majority of those species that have been observed or reported to occur in the Genesee country. No attempt has been made to report every occurrence of these minerals nor to produce a guide to specific collecting sites. All lands in the Genesee country are privately owned or are park lands. Trespassers on private lands are not generally welcome and permission must be obtained from the owner of the private lands before entry or collecting is made.

Thin, light yellow encrustations and veinlets of sulfur occur sparingly in the Lockport dolomite of the Rochester area. Crystals of sulfur are small and very rare.

Thin veinlets and fissure fillings are occasionally found in the Lockport dolomite of the Rochester area and at Lockport. Cubic crystals, sometimes modified, and up to 1/4 inch in size are very rare. The Irondequoit limestone near Wolcott, New York, contains small amounts of galena.

This mineral is common in the Lockport dolomite. Small amber colored crystals are frequently found in solution cavities and resinous brown crystalline masses that exhibit good cleavage occur as fissure fillings. The crystals include small partly transparent ones that usually have small dark inclusions. Crystals that range up to 1/2 inch in size have a shining luster and a somewhat truncated conical shape. Larger crystals up to 3/4 inch are brown and opaque with rather rough surfaces.

Sphalerite has been noted in the septaria of Bristol Valley and Bare Hill about 10 miles south of Canandaigua and has been reported in some Devonian brachiopod shells.

Small yellow and tarnished masses have been noted in chert cavities from the Reynales limestone of the Genesee Gorge and has been reported in other areas.

Pyrite is not common in the region. It is found in small amounts in some limestones and shales. Small cubic crystals occur in the Irondequoit limestone. Tiny modified crystals and druses occur in solution cavities of the Lockport dolomite. Near Leicester, a pyrite layer about three inches thick lies at the base of the Hamilton beds and contains small fossils. Nodular concretions up to 2 inches in size with radial structure and often enclosing small fossils occur at Spring Valley near Alden, New York, in the Ludlowville shale.

Thin bladed crystals of marcasite up to 1/8 inch long are often found attached to dolomite and calcite crystals at the Penfield quarry. They are striated longitudinally and are often tarnished. They have been mistaken for rutile, stibnite and acmite.

The red fossiliferous hematite layer of the Reynales formation is one of the most conspicuous features of the Genesee Gorge. It also occurs in Densmore Creek north of Norton Street and can be found on the dumps of the old iron ore beds north of the village of Ontario. The hematite in this layer occurs as red masses frequently replacing fossils. Microcrystalline hematite and specularite are reported in various places in the Clinton group.

This is a common constituent of the beach sands along Lake Ontario. Grains of magnetite can be easily separated with a magnet. Magnetite is also present in some of the pebbles and erratics found in the glacial drift.

This brown iron oxide is most usually observed as an oxidation of pyrite or other iron minerals. It has been observed in septaria. A small area of bog iron ore occurs north of Ontario, New York.

This is reported in chert cavities of the Reynales limestone in the Genesee Gorge.

Thick beds of a coarse granular halite are mined at Retsof in Livingston County.

The Lockport dolomite is the source of very choice fluorite crystals. At the Penfield quarry, the crystals attain a size of two inches and over. The cube is the dominant form with rare modifications. Colors include wine yellow and various shades of blue. Most crystals are clear and have smooth shining faces. Some crystals show color zoning and some have rough surfaces. Small clear to blue crystals occur in the Lockport dolomite at many other localities.

This is an ubiquitous constituent of all limestones. It is usually very fine grained or massive though large fossils composed of calcite will exhibit typical rhombohedral cleavage. Good scalenohedral crystals ("dogtooth spar") are abundant in the Lockport dolomite and attain a length of two inches and more. The small crystals may be clear to smoky in color while the larger crystals are pale yellow, semi-translucent at the tips and have a rough surface composed of a multitude of smaller scalenohedra in near parallel position.

Small calcite crystals have been found in calcite veins that cut the Hamilton shales of Kashong Glen near Geneva, and in the septaria of the Canandaigua Lake region. Small twinned crystals occur with celestite in the limestone near Chittenango Falls.

Travertine deposits composed of calcite are frequently found in the area notably at Mumford and at Tufa Glen. The tufa rock frequently contains impressions of leaves and twigs.

This occurs as occasional thin white encrustations on the Lockport dolomite. It fluoresces a greenish white.

This mineral is the main constituent of the Lockport dolomite. Reflections from microcleavage surfaces of minute dolomite, grains are responsible for the glistening appearance of the rock. Solution cavities in the dolomite rock are frequently lined with rhombohedral dolomite crystals. The smaller crystals are often clear and colorless. Large crystals range up to half an inch, are white to flesh colored, have a shiny luster, and often have slightly curved surfaces. Specimens of crystallized dolomite from this region rank among the finest in the world.

The dolomite rock frequently encloses residual hydrocarbons which will fluoresce light yellow under long wave ultra violet light. Fossil coral areas are especially fluorescent.

This light brown carbonate is found in some septaria.

Brown crystals up to an inch on an edge have been found in the Furnaceville hematite in the Clinton iron ores of the Clyde and Sodus Bay quadrangle.

This is reported as green spots in chert cavities in the Reynales limestone of the Genesee Gorge and as spots in the Whirlpool sandstone of the Niagara region.

This occurs as blue spots on sandstone associated with malachite and chrysocolla in the Whirlpool sandstone of the Niagara region.

Barite occurs in the Lockport dolomite as partly clear crystalline masses. It is easily confused with celestite.

This is very common in the Lockport dolomite. Terminated crystals over 4 inches long have been found at the Penfield quarry. Crystalline, bladed and coarse fibrous types are more common. The celestite is transparent to sub-translucent and the color ranges from white to light celestial blue. At Lockport, the celestite is usually white to clear and crystals are rare. Very good blue crystals up to 2 inches long and blue fibrous veins occur in the limestone near Chittenango Falls.

White to blue crystalline masses are fairly common in the Lockport dolomite. It is frequently associated with gypsum but can be distinguished by its superior hardness. The color varies from white and gray to blue. Coarsely crystalline anhydrite exhibits the typical right angle cleavage in three directions. Large masses up to 23 pounds in weight have been found at Lockport.

Massive gray to snow white gypsum is quite common in the Lockport dolomite where it is often associated with anhydrite. Selenite, the clear variety of gypsum, is found in the Lockport dolomite as large clear masses often with excellent cleavage and sometimes with crystal faces. It frequently encloses crystals of dolomite and other minerals. It is erroneously called "mica" by some.

Gray massive rock gypsum occurs in thick beds from Erie County eastward through Ontario County and is mined at several localities. Small selenite crystals are sometimes found in the rock. Selenite has also been found in cavities inside fossils (e.g. Pentamerus of the Wallington [Reynales] limestone).

Apatite (Cellophane)
Small dark brown to black pebbles and masses of amorphous cellophane ranging in size from a pea to a bean occur in the Brewer Dock limestone member of the Reynales formation. The cellophane sometimes replaces fossil fragments. Larger phosphatic nodules occur in the Oriskany sandstone at Phelps.

This is a common constituent of the Lake Ontario beach sands and the glacial drift. The sand grains are usually red to pink though other colors and colorless varieties are reported. Red garnet is also present in the igneous and metamorphic rocks of some glacial gravels and erratics.

Green epidote is sometimes noted as a constituent of some glacial gravels and erratics. Chrysocolla Spots of chrysocolla occur in the Whirlpool sandstone of the Niagara region.

Hypersthene is sometimes noted as a constituent of Lake Ontario beach sands, the glacial drift and gabbroic rocks of the glacial gravels and erratics.

Dark green monoclinic pyroxenes (chiefly aegirite and augite) occur in the beach sands of Lake Ontario, the glacial drift and as constituents of some glacial gravels and erratics.

Black prismatic crystals of hornblende with rounded ends occur in Lake Ontario beach sands and in the glacial drift.

The identification of this clay mineral requires X-ray and other refined laboratory analytical procedures. It is present in all of the Silurian and Devonian shales of the area. The Maplewood shale contains about 85% illite.

This is present in some glacial erratics and in the mica peridotite dikes near Ithaca and Syracuse where it is an alteration of olivine.

Muscovite and biotite occur in the igneous and metamorphic rocks in the glacial gravels and erratics. Phlogopite is a constituent of the mica peridotite dikes near Ithaca and Syracuse. It is also found in some marble blocks used as railroad ballast.

This dark green soft mineral is sometimes present in some of the rocks of the glacial gravels and erratics and is present in microscopic amounts in some of the Clinton strata.

Quartz is present as grains in all sandstones and some shales. Drusy crystals and gray granular masses occur in the Lockport dolomite. It is also abundant in many of the glacial gravels, cobbles and boulders.

Irregular masses of dark gray chert are abundant in some layers and coral reefs of the Onondaga limestone at Le Roy and elsewhere. Chert, chalcedony and opal occur in the Furnaceville hematite and in the Upper Reynales limestone. In the latter, the chalcedony is sometimes banded and occasionally botryoidal.

Microcline, albite, perthite (an intergrowth of microcline and albite), oligoclase, andesine and labradorite may be found in the igneous and metamorphic rocks of the glacial gravels and erratics.

While hydrocarbons are not true minerals, they are often included in the listing of the minerals of a region. The Lockport dolomite occasionally encloses residual hydrocarbons that fluoresce a light yellow under long wave ultra violet light. Fossil corals are often especially fluorescent. Sticky masses of a grease-like hydrocarbon has been noted at the Penfield quarry sometimes penetrating selenite cleavages and coating crystals of dolomite.

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