Calcite from Yellow Lake Road cut Road Cut Mineral Occurrences of St. Lawrence County, New York:
Part II: Yellow Lake Occurrence
by Dr. Steve Chamberlain and Michael Walter
This is the second in our series of articles on significant road-cut localities for mineral specimens in St. Lawrence County, New York. The Yellow Lake road-cut produced thousands of excellent specimens of calcite and dolomite starting 40 years ago, although it has not been particularly productive for the past several decades.
The Yellow Lake road-cut is on the edge of a small rise about 1.1 km northwest of the northern tip of Yellow Lake in the Town of Macomb (Fig. 1) The road-cut is on the west side of County Rt. 10 about 6.2 km north of the intersection of Rt. 10 and Rt 3 near Oxbow. The road-cut faces an open field on the east side of Rt 10, north of the intersections with Scotch Settlement Road and Hall Road, but south of the intersection with Robinson Road. It appears on the upper left corner of the Natural Dam quadrangle in the USGS 7.5 minute topographic series (1961). The calcite specimens produced from the open cavities at this road-cut are distinctive.
History
This locality was appears to have resulted from the widening of County Rt 10 that occurred in the early 1960' s. Although not the first collectors, George Robinson and Mike Hubinsky noted cavities of interest in the road-cut in the late fall of 1964 while returning to SUNY Pots dam from a day trip to the Rossie Lead mines. During their visit to SUNY Potsdam in March, 1965, Robinson persuaded his parents to visit the locality on a Saturday, and by Sunday afternoon about 500 pounds of specimens had been recovered. Hubinsky and Robinson returned the next weekend and collected another 500 lbs of specimens. Also in the 1960s, John Pietras of Rome, NY, collected hundreds of high quality specimens from the locality. Local collectors, including Ivan McIntosh, Bob Johnson, and Charlie Bowman collected at the locality during this period, as well as many others, since the locality was listed as locality 19 in Minerals of the St. Lawrence Valley (Robinson and Alverson 1971).
The evidence at the locality as it appeared in March, 2004, (Figs. 2,3) supports the reports of these early collectors that most of the exploited crystallized cavities were between the pavement and the vertical portion of the road-cut and were at, or below, the level of the paved surface of the road. These cavities were filled in by the highway department long ago. There is every possibility that future exploration could uncover additional mineralized cavities (Figs 4,5); indeed recent collecting has yielded fine specimens of calcite and dolomite (Figs.20, 21).
Geology
The locality sits on the eastern flank of a northeast-southwest trending ridge that is part of overall fold patterns in the area north of the village of Oxbow. The rock itself is a complex assemblage dominated by Grenville marbles and other metasedimentary and metavolcanic units (Van Diver 1976, 1980). Plastic flow in the marbles has resulted in complex banding with silicate lenses, rods, and boudin structures. Tectonic activity, possibly related to that which formed the nearby Rossie lead mines (Robinson et al. 2001), has produced fractures and slickensides, providing an avenue for later mineral transport and deposition.
The Yellow Lake road-cut exposes fracture-filling mineralization in the Precambrian marble (Isachsen and Fisher 1970). Locally, the white marble has complex interrelationships with dark gray Cambrian Pots dam sandstone, that contains altered clasts up to several centimeters (see Brown 1983, for a discussion of the Precambrian/Cambrian unconformity). The age of the crystallized minerals in the fractures in unknown, but is certainly much younger in age than the host rock.
Minerals
Calcite, CaC03' occurs in two generations of distinctive habit (Figs. 6,7). The first calcite crystals to form occur as white scalenohedral crystals up to 2 centimeters and as white scalenohedral {21-31} crystals up to 15 centimeters terminated by small rhombohedral faces {lOII} both formed directly on a matrix of fine-grained marble (Figs. 9, 10, 11). The larger crystals typically have a dark brown scalenohedral core. Both forms of these early scalenohedral calcite crystals are symmetrically developed. A later generation of calcite consists of sheet-like parallel growths of colorless to white to medium gray scalenohedral crystals {21-31} with pale yellow tips showing rhombohedral faces {10-11} (Figs. 8, 13, 14, 15). Individual crystals may be up to 10 centimeters tip-to-tip. Usually there is a thin rhombohedral zone containing microscopic sulfide crystals separating the main crystal from the pale yellow tip. A few of these scalenohedral crystals are twinned on (0001), but most are not. Sometimes the larger scalenohedral crystals are cavernous with myriad smaller oriented scalenohedral crystals with pale yellow tips lining the surfaces (e.g. Fig. 10). Most of the scalenohedral crystals of this generation show growth distortion of the scalenohedral faces such that two of the opposite faces are large and four of the faces are small on each end of the crystal (Figs. 12, 18) but some are symmetrically developed (Figs. 16, 17). Pale gray phantoms are occasionally encountered inside colorless or yellow scalenohedral crystals. Plates of calcite and dolomite crystals up to 40 centimeters square, perhaps larger, were recovered.
Dolomite, (Ca, Mg)C03' forms lustrous, creamy white to tan-colored, curved rhombohedral crystals up to 1 centimeter. They occur as masses attached to calcite (Figs. 20, 21, 22), sometimes as an epitactic overgrowth (Fig. 19). The largest clusters of dolomite crystals exceed 10 centimeters in maximum dimension. Some specimens show evidence of an early phase of dolomite formation, now largely altered to goethite, and the more typical later phase with the dolomite formed on the second phase of calcite.
Goethite, FeO(OH), occurs as a thin surface coating on some calcite crystals and as earthy masses up to several centimeters replacing pyrite.
Graphite, C, occurs as shiny black plates up to 1 millimeter, usually associated with quartz crystals, but sometimes embedded in minute, late-stage calcite crystals.
Marcasite, FeS2' commonly occurs as microscopic needles and plates along internal planes within calcite crystals. Some of these minute crystals are twinned. Marcasite also occurs as flattened cockscomb arrays of crystals up to several mm in masses with cub octahedral pyrite crystals.
Pyrite, FeS2' rarely occurs as microscopic cubes inside and on the surface of calcite crystals. Cuboctahedral and octahedral pyrite crystals up to 3 millimeters form crystallized masses scattered among the calcite crystals (Fig. 23). Almost all of these have completely altered to earthy goethite and have lost any trace of the original pyrite crystal faces.
Quartz, Si02' occurs as small transparent prismatic crystals to 1 centimeter in length. Generally the positive and negative rhombohedral terminations are equally developed (Fig. 24). These crystals often contain plates of graphite.
Siderite, FeC03' occurs rarely as rhombohedral crystals up to 1 centimeter with calcite (Fig. 25). Often these are coated with a. thin layer of goethite.
Paragenesis
The first mineral to form was calcite either in small white untwinned scalenohedra tending to lie sideways on the matrix or in larger white scalenohedral crystals with dark brown cores that are oriented with the c axis approximately perpendicular to the matrix. Masses of pyrite and marcasite formed toward the end of calcite crystallization. A second generation of calcite formed later on top of the first generation. These calcite crystals are colorless to white to medium gray and form sheets of parallel scalenohedral crystals joined at the girdle. There seems to be no epitactic orientation between these sheets and the underlying large scalenohedral crystals of the first calcite generation. In general the orientation of the scalenohedral crystals in each sheet is with the c axis parallel to the surface of the matrix. More pyrite and marcasite masses formed with this second generation of calcite. There was a pause in calcite crystallization during which microscopic, unoriented crystals of marcasite, and more rarely cubes of pyrite, formed sparsely on the rhombohedral terminations of the sheets of scalenohedral calcite crystals. Calcite of a pale yellow color then continued to form giving a colored tip to the scalenohedral crystals with rhombohedral terminations. Quartz and graphite formed just at the end of the crystallization of the second second general phase of calcite crystallization and occurs in localized regions on some specimens. Dolomite formed after calcite crystallization had stopped. Some of the dolomite is epitactic on rhombohedral or scalenohedral faces of the underlying calcite. Much of it formed as unoriented curved masses of crystals on the calcite. In some specimens the dolomite is partially embedded in the second phase of calcite indicating overlap of the periods of crystallization. Some specimens also show a minor earlier phase of dolomite formation, subsequently heavily weathered and replaced by goethite. The final stage in the paragenesis saw the oxidation of most of the masses of sulfides to earthy goethite and the formation of thin coatings of goethite or botryoidal calcite on the surfaces of other minerals.
Origin
The crystals of this occurrence formed in fractures and solution cavities in the Precambrian marble. The presence of graphite crystals on and embedded in quartz crystals indicates that the mineralization is relatively recent and resulted from downward percolating meteoric water that dissolved portions of the overlying marble and redeposited it in the fractures. The components of the calcite and dolomite are almost certainly from the overlying marble itself. The graphite crystals have been freed from the dissolved marble and have fallen and been carried downward through the fractures. The source of the silica in the quartz that crystallized with the graphite is silicates in the marble that are metastable at surface conditions and are weathering. Organic molecules introduced into the ground water from the roots of plants in the overlying soil zone have held the silica in solution (see Bennett and Siegel 1987; Chamberlain 1988) for several meters until bacterial attack reduced the average molecular weight of the organic complexing agents below the point where they could hold silica in solution and the quartz precipitated. The fact that the quartz crystals are largely transparent and flawless, except for the included graphite crystals, suggests that the transport of silica by organic complexing agents and its subsequent release were slow processes resulting in gradual formation of the quartz crystals from subsaturated solutions.
The dissolution of marble or limestone by ground water higWy charged with carbon dioxide by plants in the soil zone and then reprecipitation as temperature changes cause degassing of carbon dioxide from the solution is the same mechanism that forms limestone caverns. The processes whereby iron sulfide, principally pyrite, disseminated in the marble is oxidized, but then later reduced and reprecipitated as marcasite and pyrite are less clear. Normally, the oxidative weathering products of pyrite in marble are goethite and gypsum. At this occurrence, both marcasite and pyrite formed in oriented bands of microscopic crystals on the rhombohedral faces just before the final stages of calcite crystallization and macroscopic crystals of pyrite and marcasite formed concurrently in the same sulfide crystalline mass. Whatever the process, these
data indicate that the conditions for precipitation were right at the boundary between the large pyrite stability field and the much smaller marcasite stability field, that is, that the precipitating solutions were slightly acidic.
The most recent conditions have been oxidizing and most of the masses of iron sulfides have completely altered to earthy goethite. Thin coatings of goethite also formed on some of the calcite crystals. Minor calcite precipitation has continued in the form of thin stalactitic overgrowths of tan calcite on some of the calcite and dolomite crystals (e.g. Fig. 18).
A Note on Specimens
Very large numbers of distinctive and desirable specimens were collected at this locality. Good examples frequently surface as older collections are recycled. Contemporary collectors should note that some specimens from this occurrence were briefly dipped in dilute hydrochloric acid to remove goethite stains and thin crusts of stalactitic calcite-this practice is common among local collectors. Many of the calcite specimens, however, have crystals with natural faces of very high luster. Careful inspection of cleavage surfaces on the back of specimens will usually indicate whether the specimen has been subjected to acid treatment during cleaning.
Accessibility
This road-cut is accessible for collecting; however, the large vugs below the road surface have been filled in the interests of vehicular safety. Our recent collecting indicates that further exploration is likely to yield more mineralized seams and vugs that may produce additional interesting specimens.
ACKNOWLEDGEMENTS
The authors are grateful to Dr. George Robinson or Michigan Technical University for sharing some of the early history of the occurrence and to Brian Corzilius of Ithaca, NY, for preserving the material from the Pietras Collection. We thank Mike Hawkins of the New York State Museum for providing access to specimens from this locality for examination.
REFERENCES
Bennett, P. and Siegel, D. I. 1987. Increased solubility of quartz in water due to complexing by organic compounds. Nature 326:684-686.
Brown, C. E. 1983. Mineralization, mining, and mineral resources in the Beaver Creek area of the Grenville Lowlands in St. Lawrence County, New York. U.S. Geological Survey Professional Paper 1279.
Chamberlain, S. C. 1988. On the origin of "Herkimer diamonds." Rocks and Minerals 63:
454.
Isachsen, Y. W., and Fisher, D. W. 1970. Geologic Map of New York, Adirondack Sheet.
University of the State of New York, The State Education Department, Geological Survey.
Robinson, G. and Alverson, S. 1971. Minerals of the St. Lawrence Valley. Privately
published.
Robinson, G. W., Dix, G. R., Chamberlain, S. C., Hall, C. 2001. Famous mineral
localities: Rossie, New York. The Mineralogical Record 32: 273-293.
Van Diver, B. B. 1976. Rocks and Routes of the North Country. Humphrey Press, Geneva, New York.
Van Diver, B. B. 1980. Field Guide to Upstate New York. W. F. Kendall/Hall Publishing
Company, Dubuque, Iowa.
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Calcite from Yellow Lake Road cut
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