JASPER, AGATE
OR NOT?
Origins
and History
 |
| Botswana Agate at Jemel |
In ancient
times, agate was defined as the beautiful translucent and opaque banded
chalcedony found within geodes or nodules in basalt or other volcanic rock. It
was named after the Achates River (now the Drillo River) in Sicily, still a
major source, and was used by the Egyptians before 3000 B.C.
The literal
definition of jasper is “spotted or speckled stone”, though the jasper stone of
the past probably didn’t follow its definition, as jasper was most often a
green stone, spotted, speckled, or not; and may have been a green jasper as
defined in modern terms or possibly nephrite jade or chrysoprase. In time, the
typical jasper would become better known as an opaque red chalcedony often
found in association with sedimentary iron ore deposits.
Modern
Modifications
Identifying
characteristics distinguishing the two stone definitions began to emerge,
specifically: agate – cryptocrystalline quartz derived from geodes or nodules,
of volcanic origin, translucent to opaque, and displaying an organized pattern
(lines or bands, concentric circles, etc.); and jasper – amorphous or
microcrystalline quartz, massive, of sedimentary origin, opaque, and of a
consistent color or displaying an unorganized pattern (spots, speckles, dots,
blotches, etc.), or no recognizable pattern at all.
What might be considered true agates or
true jaspers still retain these definitions. However, with the great variety of
agates and jaspers currently available, including new discoveries, many cross
definition boundaries, sometimes in multiple ways and could easily be called
agate-jaspers or jasper-agates. While a cryptocrystalline (fibrous structure)
characteristic can be quite easily seen in translucent agates, it’s not easily
detected in any opaque stone, so some jaspers could also have a
cryptocrystalline structure. Because of their translucent characteristic, it
can accurately be said that agates are of volcanic origin, since sedimentary
chalcedony is generally composed of compressed quartz grains, clay, and other
impurities that make it opaque. But red, yellow, green, black, brown, and many
other jaspers can be and often are formed by volcanic processes as well as
sedimentary, so the volcanic identifier doesn’t differentiate jaspers from
agates. Chalcedony varieties with many agate characteristics are not always
confined to geodes or nodules, and neither agates nor jaspers are always
defined by translucency or opaqueness, or by organized or unorganized patterns.
Commercial
Influence
This leads us to answer the question of
who decides what names to give stones with agate, jasper, or mixed agate and
jasper characteristics. And, the answer is not always the same. Generally names
are determined either by a discoverer of a stone, a commercial entity that
first brings a stone to market, or a name simply emerges from what a group of
people or the general public begins to call it.
Usually, whoever determines the name of a
stone tries to use the given definitions as foundations or, at minimum,
guidelines for their decisions. For many stones like Brazilian Agate, Botswana
Agate, Red Jasper, Yellow Jasper, and Fancy Jasper, naming is easy because they all fit into their
definitions
well. However, stones that don’t fit well into one definition or
the other are many as well. Some examples include Moss Agate, Montana Agate,
Pigeon Blood Agate (translucent, but
unorganized pattern, and generally massive); Mexican Crazy Lace Agate, Blue
Lace Agate (wavy organized pattern, but massive as crusts and seams, and
opaque to only slightly translucent); and Bruneau
Jasper, Biggs Jasper, Picture Jasper (opaque and massive, but
wavy semi-organized pattern). Typically, it appears that if agate
characteristics are found in a chalcedony based stone, the agate name takes
precedence.
 |
| Bruneau Jasper at Jemel |
 |
| Rainforest Rhyolite at Jemel |
It is also worth mentioning that some
stones called jasper may not be jaspers at all by modern definition. The
original name for Rainforest Jasper was actually Rainforest Rhyolite. Rainforest Jasper, Leopardskin Jasper, Poppy
Jasper, Ocean Jasper, and other orbicular jaspers all have a rhyolite (some varieties perlitic,
spherulitic and massive) appearance,
so therefore are likely rhyolites. However, most rhyolites don’t take a high
polish as these stones do, so these therefore must have a high quartz content. They also actually meet the original definition of jasper – “spotted or speckled
stone” better than most jaspers of modern definition.
Caution should be taken with at least one
stone, often called jasper, which is not and should not be called jasper. While
there is a true Picasso Jasper
available, much of what is called Picasso Jasper was originally called Picasso Marble. And whether the jasper
name has resulted from confusion by an innocent or ignorant public, because the
two stones are somewhat similar in appearance, or because of some commercial modification
for increased popularity, most stones of richer color variation and beauty are,
in fact, marble, not jasper. Marble is a calcite (calcium carbonate) based
stone, not quartz/chalcedony (silicon dioxide) based. This means that, though
beautiful and attractive in its own right, Picasso Marble is much softer
(hardness = 3-3.5) than jasper (hardness = 7), and therefore not as scratch
resistant or as durable as a true jasper.
Find many of these natural stone pendants at jemelww.com
Copyright 2015 Steven
A. Barben
General References
Pough, Frederick. 1983. Peterson Field Guides: A Field Guide to Rocks and Minerals.
Houghton
Mifflin Co.
Mottana, Annibale; Crespi, Rodolfo; and Liborio, Giuseppe.
1978. Simon & Shuster’s Guide to
Rocks and Minerals. Simon &
Shuster Inc.
Note: Minor sources may include, but are not limited to
a variety of printed and online sources as well as observation and experience.
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