The Lake Valhalla Quarry, located in Montville, Morris County, New Jersey was renowned in the late 19th C for its gem grade serpentine and in more modern times for its fluorescent diopside. It is possible that this site is synonymous with "Gordon's Crystalline Limestone Quarry" as this marble outcropping appears to be unique in the Montville area (an area dominated by gneissic rocks).

A small (approximately 10 acre) deposit of marble outcropped near Turkey Mountain in Montville. A quarry was established there to provide marble for flux to the iron furnaces at nearby Boonton, NJ. A portion of the marble was also burned to provide lime for agricultural use. During quarrying operations, significant amounts of a gemmy greenish to gold serpentine was recovered admixed with the marble; apparently, much of it was initially tossed aside as waste rock. However, the potential value of the serpentine both for gemstones and decorative objects was soon recognized. While the serpentine remianed merely a by-product of marble mining, Montville serpentine did enter the market as both gemstone and carving rough.

Gemologist George F. Kunz provided a general description of the occurrence in 1892:

The golden and greenish-yellow serpentine of Montville, N. J. is of the precious variety, and takes and excellent polish. In this locality serpentine occurs associated with crystalline dolomite, and many fine specimens in different collections were obtained during the process of quarrying this rock, for burning into quicklime or for flux for iron furnaces. It occurs in small seams or veins, or in isolated nodules from a few inches to several feet in diameter. George P. Merrill of the United States National Museum has written an exhaustive paper on this subject. He has found the white and grey nuclei which often exist in the center of these nodules of serpentine are pyroxene, and by analysis and microscopic examination has proven that this serpentine is the result of an alteration to pyroxene. The beautiful series of polished specimens in the United States National Museum and in Yale University show all the changes from pyroxene to serpentine.

In 1883, Nelson Horatio Darton, an 18 year man old from Brooklyn, New York, published a lengthy piece in the Scientific American Supplement about the minerals of the site. Born in 1865, Darton apprenticed in his grandfather's pharmacy at the age of 13 and developed a sound understanding of practical chemistry. In 1886 he would join the United States Geological Survey, where he remained until his death in 1948.

Montville, Morris County, New Jersey -- This locality is an old one, and well known to mineralogists. [It occurs...]in the granular limestone, which occurs in a small isolated ridge in the gneiss within a space of ten acres, about two miles north of the railroad station of Montville, on the Boonton Branch of the Delaware, Lackawanna, and Western Railroad, and is reached by a road running north from about a mile east of the railroad station. This road branches into two at the limestone kilns, about a mile from the railroad track, and the left hand branch is taken, which leads more directly to the quarry, which is on the right hand, about a mile further on, and quite conspicuous by the loose rock lying in front of the quarry. It is on the property of a Mr. John J. Gordon, and produces a very fine limestone for use in the furnaces and forges in the vicinity, as well as lime for agricultural purposes, it being the only limestone in the vicinity for fifteen miles. Between it and its walk of gneiss occur veins of the minerals so characteristic of the locality, and for which it has become famous -- serpentine, asbestos, phlogopite, gurhofite [dolomite], pyrites, biotite, aragonite, dolomite, tremolite, and possibly others in lesser quantity.

Serpentine -- All the varieties of this species, and of every color from nearly white to black, is profusely distributed through the limestone in the lower or main quarry in veins and pockets. It is generally soft, translucent, and to be found in masses from a pea to a cubic foot in size. Much of it is of a pure oil green color, rich and translucent, making a very fine and attractive looking mineral specimen. No difficulty need be experienced in producing all the varieties of this mineral, as much has been removed and may be found in the vicinity of the quarry, as it is always carefully separated from the limestone as being useless, and thrown aside, or in some instances, when of peculiar beauty, sold as specimens. The variety of serpentine known as marmolite, which is made up of numberless plates of the mineral packed together similar to mica, but of the green color of the serpentine picolite, or fibrous serpentine, also frequently occurs of a light grass green color, and is a very interesting variety.

In selecting specimens of serpentine, care should be taken to procure that which is the most translucent, and that holding miniature veins of asbestos. These are not so plentiful as those of the pure serpentine alone, but occur in the southern end of the main quarry. The width of these veins of asbestos is seldom over an inch, but those of even much less are highly prized as specimens. These veins of asbestos are, in places, several inches in length, but are generally much broken in removing them, as their fibrous structure, at right angles to their length, makes them very fragile, and pure specimens of asbestos can seldom be found. However, they make much finer specimens when with the serpentine. Frequently these specimens may be obtained with a layer of gurhofite above them, and separated by the serpentine; this assortment is very interesting, revealing to us the manner in which they were formed, which was by a process termed segregation.

This gurhofite, called bone by the quarrymen, occurs in white, dense looking masses, intermingled with the serpentine, especially in the upper end of the quarry, where veins six and eight inches in thickness are abundant, and from which specimens may be readily obtained showing the fibrous structure of the gurhofite and the association with the serpentine, to which it is found attached; it is quite different from the limestone in appearance, and need not be mistaken for it.

Phlogopite -- In a vein near the lower end of the quarry, near the asbestos locality, occurs large plates of this mineral, which is a variety of mica, and has all of the characteristics of a pure silvery white color, and from one by three inches in area to less. It is easily separable in folia, and cannot be confounded with any of the other minerals. A huge mass of the veinstone holding abundance of this mineral is exposed, whence it may be plentifully obtained in excellent crystals.

Pyrites -- White and yellow iron pyrites are abundant in the gneissic rock adjoining the limestone, and frequently very fine, perfect crystals may be found handsomely dressed upon the rock. There is no particular portion of the quarries in which they abound.

Biotite -- This is a variety of mica in small crystals, of a dark brown color, and quite plentiful in the gneiss inclosing the veins of limestone. Up in the older quarries it is more abundant; on the north wall of the vein it is often in very fine specimens, and there even in large number, in a locality, generally a pocket in the gneiss.

Tremolite -- is quite abundant on a large mass of limestone in the extreme upper quarry, which is a short distance east of the main one, over a small hill. The tremolite occurs in white crystals, about a quarter inch in width and from a half to three inches in length. The crystals are opaque, but very smooth and glistening, lining cavities in this mass of limestone. It is a variety of hornblende, composed of silica, lime, and magnesia, with a little alumina. It probably occurs in places in the vicinity of this block, and in finer specimens, as these are frequently, when near the surface, much weathered and worn. This is a characteristic granular limestone mineral, and a very interesting one. We will again meet it when examining the New York city localities.

Aragonite -- occurs in very small masses, of a light yellow color and fibrous structure, between layers of serpentine. When they are separated by a small interspace, as it frequently is, the fibers are very large, coarse, and brittle, and thus do not resemble asbestos, although in some instances they might be mistaken for picolite, but, distinguished from it by effervescing on contact with a drop of acid, as it is a carbonate of lime, and also containing a trace of iron. I have never seen any fine specimens of it from this locality, but deeper down in the rock it may occur in greater profusion.

Dolomite -- occurs to a limited extent as such; most of it, being in the form of gurhofite crystals, may be occasionally found with aragonite of a light pearly gray color and rhombohedral crystals. As before noticed, Staten Island is the best locality for this species.

Calcite-- In places the limestone is perfectly crystallized, and of a pure white or other color, when it forms an attractive mineral, and often worth removing. The limestone of the main quarry, carefully averaged, was found to have the following chemical composition:

Lime	11.09
Magnesia	37.94
Carbonic acid	30.61
Silica	10.22
Iron and alumina	5.24
Water and loss	4.90
Total:	100.00

In places it is spotted with the serpentine, and judging from its rough state resembles "verde antique," and at that of a beautiful color; samples of this should be obtained.

Feldspar -- This mineral occurs very plentfully in the space between the limestones and gneiss. It is generally of a flesh red color and often in very perfect crystals, in some instances an inch and a half in length; as its hardness is 6, it can be readily distinguished from calcite, which it much resembles, but which has only a hardness of 3, and dissolves with effervescence in acids.

It is interesting to note that Darton makes no mention of the diopside occurring at the site; it is possible that he mistook it for tremolite, as tremolite does not appear on the species lists for the site.

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Bibliography

• Darton, Nelson Horatio
On The Mineralogical Localities In And Around New York City. Part IV
Scientific American Supplement. Vol. XVI, No. 415. December 15, 1883

• Kunz, George Frederick Gems and Precious Stones of North America
(Second Edition) Co. 1892, Scientific Publishing Co.