BRECCIA

A. Breccia cabochons (largest one, greater dimension - ca. 5 cm). Smithsonian Institution. (photo by L. Bolton)

B. Breccia bowl (greatest dimension - ca. 10 cm). Smithsonian Institution. (photo by B. Chromy)

DESCRIPTION: Breccia is the name widely applied to a diverse group of rocks that consist of angular, greater-than sand-size fragments surrounded by a finer grained matrix. The diversity depends upon the fact that breccias have several modes of origin, and consequently, both the fragments and the finer grained matrices may be of just about any composition. Consequently, the properties of breccias differ markedly from rock to rock -- see REMARKS.

OTHER NAMES: A few breccias have extents that have led to their being named according to the scheme used for stratigraphic units (see Appendix B, Glossary). Two examples are the Mackinac Breccia, which is well exposed in St. Ignace and on nearby Mackinac Island, Michigan; and the Zopilote Breccia of the Permian basin of west Texas. The following designations are, for the most part, marketplace names:

Boakite - brecciated green and red jasper from the vicinity of Tonopah, Nevada.
Breccia Pernice marble - perhaps the most widely known and utilized of many breccia marbles, this mottled pinkish orange breccia is quarried near Venice, Italy.
... breccia (e.g., jasper breccia) - designations of this kind have been given several breccias, including those used as gemrocks. The first term of such binomial names may relate to such diverse things as the rock's identity, its geological occurrence and/or some particular aspect of its appearance. Consequently, any person so-naming a breccia has much latitute. To emphasize this point -- even the rock's identity may based on the composition of its fragments, its matrix, or even some combination of the two. ... Also, if names given in the past to breccias used as gemrocks is any indication, it seems inevitable that modifying terms given in the future will be based on marketability considerations.
Brecciated ... (e.g., brecciated agate and novaculite -- see AGATE and CHERT entries) - this adjective has been applied to several gemrocks; the rock term modified usually applies to the fragments.
Chapinite - a yellow and brown breccia, made up largely of jasper fragments, from near Tiefort Village, San Bernardino County, California.
Creolite (or creolin) - one of several names given brecciated jasper.
... matrix - in some respects, gemrocks such as turquoise matrix are breccias.
Dallasite - name applied to a rock consisting of fragments of pillow lava within a matrix of tuffaceous volcanic debris from, for example, the east side of Vancouver Island, British Columbia and found on some of the beaches near Point Roberts, Whatcom County, Washington.
Jasper breccia - term applied to two different materials: 1.breccias the larger fragments of which are jasper and 2.breccias that have been jasperized.
Mosaic ... (e.g., mosaic agate -- see AGATE and TRAVERTINE entries). This adjective has been applied to several gemrocks that exhibit fragmentization or brecciation.
Ocean-picture rock - "Local name for a brownish, brecciated, carbonate-bearing silicified serpentinite with veinlets of pale blue to white quartz [that] occurs near Midway, British Columbia, near Washington border" (Mitchell, 1985).
Pietersite (also called pseudocrocidolite) - name given to a brecciated gemrock from Namibia (formerly Southwest Africa); see HAWK'S-EYE ... entry.
Ruin agate - name sometimes given to brecciated agate, certain surfaces of which resemble ancient ruins (see AGATE entry).
Ruin aragonite - brecciated "Mexican onyx" with relations similar to those of ruin agate (see AGATE entry) and ruin marble (see TRAVERTINE entry).
Ruin marble - limestone breccia, which when cut in certain directions, has an appearance that resembles ancient ruins (see MARBLE entry).
Verde antique (serpentine marble) breccia - a so-designated rock has been quarried at the classical Casambala locality near Larissa, Thessalia, Greece.
Verdolite - a talcose-dolomitic breccia from New Jersey.
Youngite - brecciated chalcedony-jasper rocks -- e.g., the gemrock from the vicinity of Guernsey, Platte County, Wyoming that consists of red and yellow jasper fragments within a matrix of off-white to grayish chalcedony .

USES: Beads; cabochons for various pieces of jewelry, particularly relatively large ones such as brooches and belt buckles; paperweights and bookends; diverse vessels (see Figure B); carvings; etc.

OCCURRENCES: Breccias occur in several diverse environments where angular rock fragments have been enclosed in a finer grained matrix and lithified -- see REMARKS.

NOTEWORTHY LOCALITIES: See those given under the OTHER NAMES subheading.

REMARKS: The term breccia, according to OED, has its roots in the Old Teutonic brekan (to break) and comes from the Italian where it was "used in the name Breccia Marble before its separate use [as a rock name] in Geology." The Italian apparently meant in a literal sense "gravel or rubbish of broken walls" (ibid.).

Geologically, most breccias are either lithified rubble -- e.g.,lithified sediments or pyroclastic deposits that consist to a noteworthy extent of pebble- to boulder-sized angular fragments -- or were formed by crushing and grinding within fault zones. These breccias are generally referred to as sedimentary breccias and cataclastic (or fault) breccias, respectively. However, many breccias, including those used as gemrocks, have been formed as the result of other processes -- e.g., desiccation, which involves cracking as the result of dehydration or drying an subsequent filling of the cracks to give the overall mass a coherence. Indeed, in his "Dictionary of Rocks" (1985), my good friend Dick Mitchell (1929-1989), to whose memory I dedicated "Minerals of Virginia, 1990," has 62 entries (more than two pages!) of names that he found applied to breccias; most relate to genesis, a few are only descriptive.

In any case, it seems very likely that breccias other than those listed under the OTHER NAMES subheading have been or in the future will be used at least locally as the rough for fashioning ornamental and curio stones. And, whatever their origins or compositions, I suspect several will be given so-to-speak marketplace names rather than the names on Mittchell's list. Also, I suspect that even though most breccias used as gemrocks will be chosen because they are considered attractive, some will be fashioned and marketed because of their potential appeal as conversation pieces -- e.g., impact breccias.

SIMULANTS: I know of nothing that has been produced and represented falsely as breccia or even substituted for breccia so far as its use in fashioned gemrock pieces. However, considering how closely some terrazzos resemble breccias, I suspect someone will (perhaps already has) made terrazzo masses with dimensions such that they could be fashioned into items that resemble those fashioned from breccia.... It would seem that such masses of terrazzo could be carved or otherwise fashioned at least as easily as similarly appearing breccias. Furthermore, it would seem that terrazzo could even be cast into desired forms. - [If the ingredients for the terrazzo were scrupulously chosen to avoid detection, distinguishing such pieces from those fashioned from natural breccias could be virtually impossible, at least by macroscopic means.].

REFERENCES: No general reference.

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