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(4) LOOSE / ROUGH
STONES
LIMB CASTS / PETRIFIED WOOD
CONIFER?
7cm X 7cm X 8cm
9.5oz
9cm X 7cm X 4cm
5.2oz
AGATIZED / GEM POCKETS
PALM WOOD? OR JASPER?
VUG INCLUDED
9cm X 5cm X 5cm
7.3oz
LONG EDGE PIECE
14cm X 3cm X 2cm
8.2oz
FLOURESCENT
LONG & SHORT WAVE
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FYI
A lapidary (the word means "concerned with stones") is an artist or artisan who forms stone, mineral, gemstones, and other suitably durable materials (amber, shell, jet, pearl, copal, coral, horn and bone, glass and other synthetics) into decorative items such as engraved gems, including cameos, or cabochons, and faceted designs. Hardstone carving is the term in art history for the objects produced and the craft. Diamond cutters are generally not referred to as lapidaries, due to the specialized techniques which are required to work diamond. Gemcutter typically refers to diamond cutters or producers of faceted jewels in modern contexts, but artists producing engraved gems, jade carvings and the like in older historical contexts.
The arts of a sculptor or stonemason do not generally fall within the definition, though chiseling inscriptions in stone, and preparing laboratory 'thin sections' may be considered lapidary arts. But, figurative engraved gems and cameos are certainly the work of artists. In modern contexts, the term is most commonly associated with jewelry and decorative household items (e.g. bookends, clock faces, ornaments, etc.) A specialized form of lapidary work is the inlaying of marble and gemstones into a marble matrix, known in English as "pietra dura" for the hardstones like onyx, jasper and carnelian that are used, but called in Florence and Naples, where the technique was developed in the 16th century, opere di commessi. The Medici Chapel at San Lorenzo in Florence is completely veneered with inlaid hard stones. The specialty of "micromosaics", developed from the late 18th century in Naples and Rome, in which minute slivers of glass are assembled to create still life, cityscape views and the like, is sometimes covered under the umbrella term of lapidary. In China, lapidary work specializing in jade carving has been continuous since at least the Shang dynasty.
Apart from figurative carving, there are three broad categories of lapidary arts. These are the procedures of tumbling, cabochon cutting, and faceting. The distinction is somewhat loose, and leaves a broad range within the term cabochon. The picture to the left is of a rural, commercial cutting operation in Thailand. This small factory cuts thousands of carats of sapphire annually.
Most lapidary work is done using motorized equipment and resin or metal bonded diamond tooling in successively decreasing particle sizes until a polish is achieved. Often, the final polish will use a different medium, such as tin oxide, glasitite or cerium(IV) oxide. Older techniques, still popular with hobbyists, used bonded grinding wheels of silicon carbide, with only using a diamond tipped saw. Diamond cutting, because of the extreme hardness of diamonds, cannot be done with silicon carbide, and requires the use of diamond tools.
There are also many other forms of lapidary, not just cutting and polishing stones and gemstones. These include: casting, faceting, carving, jewellery, mosaics (eg. little slices of opal on potch, obsidian or another black stone and with a clear dome (glass or crystal quartz) on top. There are lapidary clubs throughout the world. In Australia there are numerous gemshows including an annual gemshow, the Gemborree which is a nation-wide lapidary competition. There is a collection of gem and mineral shows held in Tucson, Arizona, at the beginning of February each year. This group of shows constitutes the largest gem and mineral event in the world. The event was originally started with the Tucson Gem and Mineral Society Show and has now grown to include dozens of other independent shows.
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Petrified wood (from Ancient Greek πέτρα meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement. The organic materials making up cell walls have been replicated with minerals (mostly silica in the form of opal, chalcedony, or quartz). In some instances, the original structure of the stem tissue may be partially retained. Unlike other plant fossils, which are typically impressions or compressions, petrified wood is a three-dimensional representation of the original organic material.
The petrifaction process occurs underground, when wood becomes buried in water or volcanic ash. The presence of water reduces the availability of oxygen which inhibits aerobic decomposition by bacteria and fungi. Mineral-laden water flowing through the sediments may lead to permineralization, which occurs when minerals precipitate out of solution filling the interiors of cells and other empty spaces. During replacement, the plant's cell walls act as a template for mineralization. There needs to be a balance between the decay of cellulose and lignin and mineral templating for cellular detail to be preserved with fidelity. Most of the organic matter often decomposes, however some of the lignin may remain. Silica in the form of opal-A, can encrust and permeate wood relatively quickly in hot spring environments. However, petrified wood is most commonly associated with trees that were buried in fine grained sediments of deltas and floodplains or volcanic lahars and ash beds. A forest where such material has petrified becomes known as a petrified forest.
Formation
Petrified wood forms when woody stems of plants are buried in wet sediments saturated with dissolved minerals. The lack of oxygen slows decay of the wood, allowing minerals to replace cell walls and to fill void spaces in the wood.
Wood is composed mostly of holocellulose (cellulose and hemicellulose) and lignin. Together, these substances make up 95% of the dry composition of wood. Almost half of this is cellulose, which gives wood much of its strength. Cellulose is composed of long chains of polymerized glucose arranged into microfibrils that reinforce the cell walls in the wood. Hemicellulose, a branched polymer of various simple sugars, makes up the majority of the remaining composition of hardwood while lignin, which is a polymer of phenylpropanes, is more abundant in softwood. The hemicellulose and lignin encrust and reinforce the cellulose microfibrils.
Dead wood is normally rapidly decomposed by microorganisms, beginning with the holocellulose. The lignin is hydrophobic (water-repelling) and much slower to decay. The rate of decay is affected by temperature and moisture content, but exclusion of oxygen is the most important factor preserving wood tissue: Organisms that decompose lignin must have oxygen for their life processes. As a result, fossil wood older than Eocene (about 56 million years old or older) has lost almost all its holocellulose, and only lignin remains. In addition to microbial decomposition, wood buried in an alkaline environment is rapidly broken down by inorganic reactions with the alkali.
Wood is preserved from decomposition by rapid entombment in mud, particularly mud formed from volcanic ash. The wood is then mineralized to transform it to stone. Non-mineralized wood has been recovered from Paleozoic formations, particularly Callixylon from Berea Sandstone, but this is very unusual. The petrified wood is later exposed by erosion of surrounding sediments. Non-mineralized fossil wood is rapidly destroyed when exposed by erosion, but petrified wood is quite durable.
Some 40 minerals have been identified in petrified wood, but silica minerals are by far the most important. Calcite and pyrite are much less common, and others are quite rare. Silica binds to the cellulose in cell walls via hydrogen bonding and forms a kind of template. Additional silica then replaces the cellulose as it decomposes, so that cell walls are often preserved in great detail. Thus silicification begins within the cell walls, and the spaces within and between cells are filled with silica more gradually. Over time, almost all the original organic material is lost; only around 10% remains in the petrified wood. The remaining material is nearly pure silica, with only iron, aluminum, and alkali and alkaline earth elements present in more than trace amounts. Iron, calcium, aluminum are the most common, and one or more of these elements may make up more than 1% of the composition.
Just what form the silica initially takes is still a topic of research. There is evidence of initial deposition as opal, which then crystallizes to quartz over long time periods. On the other hand, there is some evidence that silica is deposited directly as quartz.
Wood can become silicified very rapidly in silica-rich hot springs. While wood petrified in this setting is only a minor part of the geologic record, hot spring deposits are important to paleontologists because such deposits sometimes preserve more delicate plant parts in exquisite detail. These Lagerstätte deposits include the Paleozoic Rhynie Chert and East Kirkton Limestone beds, which record early stages in the evolution of land plants.
Most of the color in petrified wood comes from trace metals. Of these, iron is the most important, and it can produce a range of hues depending on its oxidation state. Chromium produces bright green petrified wood. Variations in color likely reflect different episodes of mineralization. In some cases, variations may come from chromatographic separation of trace metals.
Wood can also be petrified by calcite, as occurs in concretions in coal beds. Wood petrified by calcite tends to retain more of its original organic material. Petrification begins with deposition of goethite in the cell walls, followed by deposition of calcite in the void spaces. Carbonized wood is resistant to silicification and is usually petrified by other minerals. Wood petrified by minerals other than silica minerals tends to accumulate heavy metals, such as uranium, selenium, and germanium, with uranium most common in wood high in lignin and germanium most common in wood preserved in coal beds. Boron, zinc, and phosphorus are anomalously low in fossil wood, suggesting they are leached away or scavenged by microorganisms.
Less commonly, the replacement minerals in petrified wood are chalcocite or other sulfide minerals. These have been mined as copper ore at locations such as the Nacimiento Mine near Cooba, New Mexico.
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