LEOPARDITE & LEOPARD ROCK

LEOPARDITE & LEOPARD ROCK (See also PORPHYRY entry.)

A & B. Leopardite carving (height - ca. 30 cm) by an unknown sculptor; this leopardite, from Belmont, Gaston County, North Carolina is in the office of the director of the North Carolina State Museum of Natural Sciences in Raleigh, North Carolina. (© photo by Karen DeBord)

C. Plume agate (cube edge - 5.1 cm) that consists of dark gray to black "three dimensional dendrites" of manganese hydroxide within light colored chalcedony from Runion Agate mine, near Bentonville, Warren County, Virginia. Current location of this cube is unknown. Notice how the leopardite spotlike appearance on the top surface of this cube is merely the expression of the elongate dendritic shaped zones displayed on the right side. -- An apparently similar relationship was recognized by Hunter (1853) in the leopardite from Charlotte, North Carolina: "when broken diagonally, it presents a handsome arborescent appearance"; also, cf. Plate VIII A & B in Watson, Laney, and Merrill (1906). (© photo by T.M. Gathright, II)

D. Leopard rock. Porphyritic gabbro in Ombepera River, Epupa Complex, northwestern Namibia. (© photo by Alfred Kröner, University of Mainz, Germany)

E. Leopard rock. Porphyritic diabase (width - 27 cm) from glacial deposit at Hubscher & Son sand and gravel pit, Isabella County, Michigan. Dietrich garden, Mount Pleasant, Michigan. (© photo by Dick Dietrich)

DESCRIPTION: Leopardite is a widely recognized rock name that was introduced into the geological literature in the mid 1800s (see REMARKS). Various descriptions of this rock in the literature can be summarized as follows: off-white, fine-grained aplite (or alaskite), with sporadic quartz phenocrysts, that is characterized by dark gray to black or brownish, roughly rod-shaped zones pigmented by hydroxides of manganese (plus or minus iron). Unfortunately, however, subsequent use of this name and of the descriptive term leopard rock has led to a nomenclature nightmare.

In the past, both of these designations were once used fairly consistently: Leopardite, although extended to include rocks other than those like the type material, was usually applied to rocks that roughly resemble leopards' coats -- i.e., spotted rocks with dark spots surrounded by a lighter colored matrix. Leopard rock was usually used as a descriptive designation for spotted rocks with the opposite color relationships -- i.e., rocks with light colored spots surrounded by a darker matrix. Today, however, both designations are frequently applied to either color relationship and, in some cases, both names have been applied to the same individual rocks; and, this use of the terms occurs in both the geological literature and in the world of the lapidary marketplace.

Thus, it seems, one needs to bow to the use whereby both terms are applied to just about any spotted rock that even roughly resembles the pattern of leopards' coats -- either directly or inversely. However, herein, in order to facilitate presentation of the following two general descriptions, I revert to the former general usage: the first, labeled Lepardite, relates to material from the type locality as an example of those spotted rocks, the spots of which are dark colored and surrounded by a light colored matrix; the second, labeled Leopard rock, refers to these "spotted" rocks, the color arrangments of which are the opposite of those of leopardite (and leopards!) -- i.e., light colored spots surrounded by a dark colored matrix.

         Leopardite -- relatively fine-grained porphyritic (quartz phenocrysts) alaskite with relatively closely spaced, roughly rod-shaped dark colored zones that are so-to-speak pigmented by manganese and/or iron oxides.
            Colors - the alaskitic rock is off-white; the dark colored rod-shaped zones are dark gray to black or, less commonly, brownish; the "rods" appear as spots on relatively flat planes that transect their lengths (see Figure C).
            H. (effective hardness) 6-7, but some rocks referred to as leopardite have hardnesses that range much lower.
            S.G. 2.62 -2.66 (for type material, not for other rocks so-named)
            Light transmission - opaque
            Luster - overall dull to pearly (or even subvitreous for some of the so-named rocks with these color relations)
            Breakage - irregular
            Miscellany - small quartz and/or feldpsar phenocrysts occur sporadically in the so-called alaskite porphyry that constitutes the main mass of the type leopardite; other so-named rocks have diverse additional properties.

        Leopard rocks -- Rocks certain surfaces of which are dark colored and spotted with lighter colored, typically globular-shaped areas -- i.e., the color interrelationships are the roughly the opposite of those of leopardite and leopards' coats.
            Color - the dark colored matrix is commonly dark gray to nearly black, rarely reddish, brownish, etc.; the lighter colored masses are commonly off-white, tan or cream colored.
          H. (effective hardness values for most of these rocks) 6 - 7, but significantly lower for some of these rocks
            S.G. (as above) 2.5 - 4.
            Light transmission - typically opaque
            Luster - dull to subvitreous
            Breakage - irregular to subconchoidal.

OTHER NAMES: As already noted, several diverse rocks have been called leopardite and/or leopard rock. Readers who desire descriptions of these rocks should read descriptions of the named rocks -- e.g., gabbro and lapilli -- in a basic petrography book (e.g., Dietrich and Skinner, 1979). Examples of these diverse rocks follow:

I. Those called Leopard rock:

Carbonate rock layer(s) associated with phylloid algal bioherms - "an unofficial term used to describe a carbonate rock layer(s) associated with phylloid algal bioherms in [, for example,] the Holder Formation of the Sacramento Mountains. I think that the term was
put forth by members of the carbonate research group at Shell in the 1960's ... Leopard rock usually shows up below the large phylloid algal bioherms as a layer or in small (1-2 m) mini-bioherms. The outer surface is an irregular, mottled pattern of reddish spots and dark gray to black spots. These spots vary from one to several centimeters in diameter." (Brenda Kirkland, personal communication, June, 2005)
Diabase, porphyritic (also porphyritic dolerite) -- "distinctive 'leopard rock' dikes, essentially a porphyritic diabase dike in which the interior zones of the dikes contain concentrations of large (up to 10 cm diameter) white subhedral plagioclase phenocrysts [in Beartooth Mountains of southern Montana] ... Dike (sic) essentially identical in appearance are found in the northern Bighorn Mountains [northcentral Wyoming], approximately 150 km to the southeast." (mason.gmu.edu/~sharlan/ mafic_dikes_beartooth_mountains) See also, Figure E.
Gabbro, feldspathic -- "Leopard rock is a coarse-grained feldspathic gabbro spotted with 6- to 15-cm. aggregates of altered plagioclase" in the Labrador trough of the Ahr Lake area, Quebec (Baragar, 1960).
Gabbro, porphyritic -- porphyritic gabbro in Ombepera River, Epupa Complex, northwestern Namibia (formerly South-West Africa) -- see Figure D.
Pegmatite -- "pegmatitic rocks associated with apatite veins of Ontario and Quebec." (Dictionary of Mining, Mineral, and Related Terms)
Serpentine -- rock described as a "hard" creamy to yellowish green serpentine with black "blotches" that occurs in Nyanga and Ruwa, Zimbabwe (formerly Rhodesia) (ww.guruve.com & www.ventureimports.com). Photographs indicate the "blotches" to range from fairly regular to extremely irregular, the latter ones not even roughly resembling leopard spots.)
Syenite (and syenite gneiss/schist) -- "light-colored variety of syenite, from Ottawa County, Ontario, Canada, containing cylindrical segregations of mafics, esp. green pyroxene; when cut properly the rock has a leopard-spot appearance." (Mitchell, 1985) [and] "Syenite gneiss consisting of ellipsoidal lumps measuring several inches across and separated by material that is mainly greenish pyroxene. The rock may be slightly schistose." (Dictionary of Mining, Mineral, and Related Terms)

II. Those called Leopardite:

... breccia? - "known in the Andes as leopardite, brown serpentine emulates the big cat's spots" (www.novica.com/); photographs of pieces fashioned from this rock from Peru qppear to be breccia.

Gabbro ("orbicular gabbro diorite") -- considering its source -- the Cooleemee Plantation, Davie County, North Carolina -- this rock, despite the given designation, could be the same general rock as the type rock from Charlotte. (http://www.itpi.dpi.state.nc.us/counties/) Corsite, an orbicular gabbro from Santa Lucia de Tallano, Corsica also has the characteristic pattern of leopardite (see Mitchell, 1985, photograph on page 55); this rock has also been called napoleonite and Corsican granite (Mitchell, ibidem).

Lapilli -- "green monolithic lapilli breccia. Breccia fragments are light, creamy green, sub-angular to rounded, matrix is darker green" recorded as occurring in Karp claim area of Bryce and Tudhope townships, near Kirkland Lake, Ontario, Canada (www.claimlake.com)

Serpentine that contains chromite nodules, apparently from Zöblitz in the Erzgebirge of Saxony, Germany -- "Cromite nodulare in serpentino ('leopardite') ... Soblitz, Sassonia" - www,dmp.uipd.it/Nimis/GuidaMinerali/Ossidi)

The preceding list indicates, rather clearly I think, that use of either of these terms is of little use other than to indicate that some surfaces of the so-named rock roughly resemble, either directly or inversely, the overall appearance of a leopard's hide. This disturbs me because, as previously implied, until rather recently, I was under the impression that used in its broad context leopardite was usually applied to rocks, which like the type rock, are characterized by surfaces exhibiting dark spots surrounded by a lighter colored matrix, whereas leopard rock was usually applied to rocks with the opposite relationships -- i.e., spotted rocks characterized by light spots surrounded by a darker matrix. Consequently, and despite the fact this generalization still appears to prevail in some people's minds, it now appears to me that there are so many published exceptions that it would seem foolhardy even to try to establish this, or any other system, as a standard usage so far as giving esclusive definitions to either of these terms.

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Some aFdditional "other names," most of which are from VanLandingham (1962, pt.9) also seem noteworthy. Those with their names preceded by an asterisk have also been called spotted lavas. Again, descriptions of the kinds of rocks on the list can be found in basic petrography books -- e.g., Dietrich and Skinner (1979).

Algoman feldspar porphyry from "many hundreds of scattered localities in the Precambrian crystalline complex of Ontario"

*Andesite (?) porphyry from east of Ramore, Ontario

Argillaceous limestone from West York, York County, Pennsylvania

*Basalt porphyry from Cooke City mining district, Park County, Montana

*Feldspar basalt porphyry from the Sioux Lookout area, District of Kenora, Ontario

"Leopard stone" is a name given "Dolomite full of worm castings set in a gray matrix and containing chert
nodules, near the base of the Upper Cambrian, Scotland." ( Dictionary of Mining, Minearl, and Related Terms)

Quartz syenite from west of Wausau, Marathon County, Wisconsin

Timiskaming silt rock from west of Makwa station on the Canadian National Railroad, District of Sudbury, Ontario

USES: Fashioned as cabochons for relatively large pieces of jewelry such as brooches; small carvings, including fetishes; diverse ornaments and functional items such as bookends and paperweights.

OCCURRENCES: Leopardite of the type locality and nearby occurrences appears to constitute portions of dikelike masses, and the dark rodlike zones are thought to be analogous to dendritic masses and thus to represent post-solidification deposition from percolating groundwater. The other kinds of rocks called leopardite and/or leopard rock have many diverse origins -- far too many to discuss here; those interested in the origins of any of these rocks should check the origins of the listed rock types in some standard petrolography or petrology book(s) or in articles about the individual rocks.

NOTEWORTHY LOCALITY: Leopardite sensu stricto occurs within and near Charlotte, Mecklenburg County and similar rocks are said to occur elsewhere within the same region. Several localities are noted for the other rocks listed under the OTHER NAMES subheading. In addition, several of these rocks have also been found as cobbles and boulders along Great Lake beaches and in glacial drift -- e.g., here and there in southern Ontario and the northcentral United States.

REMARKS: Leopardite from Charlotte, North Carolina was called the "leopard stone of Charlotte, N.C" by Professor Charles Upham Shepard (1852); he included it under his feldspar heading and described it as a "composition of compact feldspar and quartz, the spots being produced by the oxyds of iron and manganese." So far as I have been able to determine, C.L. Hunter (1853, p.377) appears to be the first one to have used the designation leopardite in print: "When broken at right angles to the pervading stripes, this mineral [sic] presents the singular spotted appearance which has given origin to the name 'leopardite.' [and, he goes on to say] As this name is quite characteristic of a rather unique rock, I would suggest the propriety of retaining its popular designation." Thus, it appears that the name actually originated with its use by residents of the area.

In addition to the diverse rocks listed under the OTHER NAMES subheading, lapidaries have encountered and fashioned diverse items from so-called leopard opal, leopard jade, leopardskin rhyolite and leopard skin jasper. However, only the items fashioned from leopard skin jasper, some of which resembles the color and pattern of leopards rather closely, have had noteworthy distribution.

Leopardite quarried in the Belmont section of Charlotte is North Carolina's representative among the nearly 200 commemorative "stones," including at least one from each of the 50 states, mounted inside the Washington Monument.

As I have looked at several of these rocks and photographs of several others, including things fashioned from them, I have sometimes wondered if those used as gemrocks might have gained a larger audience (and market) if they had been named cheetah rock, jaguar rock or ocelot rock -- my musings suggested to me that cheetah rock would be a poor choice (caveats emptor), that jaguar rock would probably gain attention of few other than members of the Judge advocate general offices, or perhaps fans of the J.A.G. TV series, but that ocelot rock might be a big seller -- say that aloud and think about it!

SIMULANT:

Plume agate - material, such as that illustrated (Figure C), roughly resembles but, in my opinion, is much more attractive than leopardite. - [Cryptocrystalline character of the lighter component differs markedly from that of leopardite.].

REFERENCES: VanLandingham, 1962, pt.9.; Watson, Laney & Merrill, 1906.

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