A. Breccia cabochons (largest one,
- 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
to a diverse group of rocks that consist of angular, greater-than
sand-size fragments surrounded by a finer grained matrix. The diversity
the fact that breccias have several modes of origin, and consequently,
the fragments and the finer grained matrices may be of just about any
Consequently, the properties of breccias differ markedly from rock to
OTHER NAMES: A few breccias have extents
have led to their being named according to the scheme used for
units (see Appendix B, Glossary). Two examples are the Mackinac
which is well exposed in St. Ignace and on nearby Mackinac Island,
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.
Pernice marble - perhaps the most widely known and utilized of many
breccia marbles, this mottled pinkish orange breccia is quarried near
- ... 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.,
agate and novaculite -- see AGATE and CHERT entries) - this adjective
been applied to several
gemrocks; the rock term modified usually applies to the
- Chapinite - a yellow and brown breccia, made
largely of jasper fragments, from near Tiefort Village, San Bernardino
- Creolite (or creolin) - one of several
names given brecciated
- ... 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
of tuffaceous volcanic debris from, for example, the east side of
Island, British Columbia and found on some of the beaches near Point
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
gemrocks that exhibit fragmentization or brecciation.
- Ocean-picture rock - "Local name for a
brecciated, carbonate-bearing silicified serpentinite with veinlets of
pale blue to white quartz [that] occurs near Midway, British Columbia,
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
agate, certain surfaces of which resemble ancient ruins (see AGATE
- Ruin aragonite - brecciated "Mexican onyx"
similar to those of ruin agate (see AGATE entry) and ruin marble (see
- Ruin marble - limestone breccia, which when
in certain directions, has an appearance that resembles ancient ruins
(see MARBLE entry).
- Verde antique (serpentine marble) breccia - a
so-designated rock has
quarried at the classical Casambala locality near Larissa, Thessalia,
- Verdolite - a talcose-dolomitic breccia from
- Youngite - brecciated chalcedony-jasper rocks
-- e.g., the gemrock from the
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
environments where angular rock fragments have been enclosed in a finer
grained matrix and lithified -- see REMARKS.
NOTEWORTHY LOCALITIES: See those given
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
before its separate use [as a rock name] in Geology." The Italian
apparently meant in a literal sense "gravel or rubbish of broken walls"
Geologically, most breccias are
rubble -- e.g.,lithified sediments or pyroclastic deposits that
consist to a noteworthy extent
to boulder-sized angular fragments -- or were formed by crushing and
within fault zones. These breccias are generally
referred to as sedimentary breccias and cataclastic (or fault)
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
or drying an subsequent filling of the cracks to give the overall mass
coherence. Indeed, in
his "Dictionary of Rocks" (1985), my good friend Dick Mitchell
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
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update: 9 July 2005
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