Gemstones 

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Absorption Spectrum


An absorption spectrum is the pattern produced when certain wavelengths of light are absorbed by a substance. In gemology, it is observed by examining a gemstone with a spectroscope. The spectrum displays both transmitted and absorbed portions of light. Dark areas indicate absorbed wavelengths. These features reveal important information about the gemstone.


Each gemstone produces a characteristic absorption spectrum. The exact pattern depends on chemical composition and crystal structure. Trace elements frequently influence the appearance of the spectrum. Different gemstones therefore generate distinctive spectral signatures. These signatures assist in identification and classification.


Gemologists rely on absorption spectra as a non-destructive testing method. No damage is caused to the gemstone during examination. The technique allows valuable information to be obtained quickly. It is especially useful when distinguishing similar gemstones. Many laboratory procedures include spectroscopic analysis.


The absorption spectrum often contains bands and lines of varying intensity. Some are broad and easy to observe. Others are faint and require careful examination. High-quality instruments improve visibility and accuracy. Skilled interpretation is essential for reliable results.


Absorption spectra demonstrate the close relationship between gemstones and light. They explain how gemstones acquire their colors and optical properties. Understanding these spectra enhances gemstone identification. It also deepens appreciation for the science behind gemstone beauty. Consequently, absorption spectra remain fundamental to modern gemology.
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Gemstones - Accarbaar
Accarbaar is a southeastern Asiatic name for black coral. The term is traditionally associated with ornamental coral materials used in jewelry. Black coral differs significantly from reef-building corals in appearance. Its dark color gives it a distinctive and elegant character. The material has long been valued for decorative purposes.
Black coral is not actually a stone but an organic material produced by marine organisms. Colonies grow slowly in ocean environments over many years. The skeleton of the organism is harvested and polished for use. Its natural dark coloration makes it unique among jewelry materials. Polished specimens often display an attractive luster.
Throughout history, black coral has been used in carvings, beads, and ornaments. Various cultures attributed symbolic and protective qualities to it. Its rarity contributed to its desirability. Skilled artisans transformed the material into intricate decorative objects. Many antique pieces remain highly collectible today.
The term accarbaar is closely related to the name akabar, another designation for black coral. Regional names often developed through local trade and cultural traditions. Such terminology reflects the historical movement of gemstones and ornamental materials. Understanding these names helps researchers interpret older gemological references. It also preserves valuable historical knowledge.
Accarbaar occupies a unique place in gemological literature. Although organic rather than mineral, it is frequently discussed alongside gemstones. Its beauty and rarity have ensured continued interest among collectors and jewelry enthusiasts. Proper conservation is important because black coral populations grow slowly. Therefore, accarbaar remains an interesting and significant gemological term.

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Gemstones - Accidental Pearl
An accidental pearl is another name for a genuine natural pearl. It forms without any deliberate human intervention. Unlike cultured pearls, accidental pearls develop entirely through natural processes. They originate when an irritant becomes trapped within a mollusc. Layers of nacre gradually accumulate around the irritant over time.
Natural pearl formation is a rare event in nature. Most molluscs never produce pearls of gem quality. The process occurs unpredictably and may take many years. Environmental conditions influence the pearl’s development. As a result, high-quality natural pearls are exceptionally scarce.
Historically, accidental pearls were highly prized because of their rarity. Before the development of pearl culturing techniques, all pearls were naturally formed. These pearls were sought after by royalty and wealthy collectors. Their value often exceeded that of many gemstones. Fine specimens became treasured heirlooms.
The term accidental pearl is not widely used in the modern pearl trade. Many professionals prefer the term natural pearl because it is more precise. The word accidental may create confusion regarding the pearl’s origin. Modern gemological laboratories generally classify pearls as natural or cultured. This terminology provides greater clarity and consistency.
Despite its limited usage, the term accidental pearl remains part of gemological literature. It reflects an earlier attempt to distinguish naturally formed pearls from cultured varieties. Understanding the term helps readers interpret historical references. It also provides insight into the evolution of pearl terminology. Consequently, accidental pearl remains a noteworthy historical expression.

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Gemstones - Acetylene Tetrabromide
Acetylene tetrabromide is a heavy chemical liquid with the formula C₂H₂Br₄. It possesses a specific gravity of approximately 2.964 at 20 degrees Celsius. The liquid has historically been used in gemological testing. Its density makes it useful for certain laboratory applications. Gemologists have employed it as a heavy liquid for density determination.
Heavy liquids are valuable tools in gemstone identification. They allow minerals to be separated according to specific gravity. Stones with lower density may float while denser materials sink. This property helps narrow identification possibilities. Such methods have long been part of gemological practice.
The density of acetylene tetrabromide can be adjusted through dilution. Various substances may be added to lower its specific gravity. This flexibility allows the liquid to accommodate different testing requirements. Controlled adjustments improve its usefulness in laboratory work. Precision is essential during such procedures.
Modern gemological laboratories often employ advanced instruments for density measurement. Nevertheless, heavy liquids remain important in certain situations. They provide a practical and relatively simple means of analysis. Historical gemological literature frequently references their use. Understanding these methods contributes to a broader appreciation of gemological science.
Acetylene tetrabromide occupies a significant place in traditional gemstone testing. Its properties made it a valuable laboratory aid for many years. Knowledge of such materials helps explain the development of gemological techniques. It also illustrates the scientific foundations of gemstone identification. Consequently, the substance remains noteworthy in gemological history.

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Gemstones - A or A.U.
A or A.U. is an abbreviation for Angström unit, commonly represented by the symbol A. It is a scientific unit used to measure extremely small lengths. In gemology, it is often associated with wavelengths of light. An example of its use is the notation 7900 A. This unit appears frequently in older gemological references.
The Angström unit plays an important role in the study of gemstone optics. Different wavelengths of light correspond to different colors within the visible spectrum. Gemologists use these measurements to analyze how gemstones interact with light. Spectroscopic testing often relies on wavelength measurements for identification. Accurate measurements help distinguish one gemstone from another.
Light absorption patterns are significant in gemstone examination. Certain gemstones absorb specific wavelengths of light while transmitting others. These characteristics create unique spectral signatures. Angström measurements help describe these patterns precisely. Such information is valuable when identifying natural and synthetic gems.
Modern scientific instruments often use nanometers instead of Angströms. Nevertheless, many classic gemological books and reports still use the older unit. Gemologists must therefore understand both systems of measurement. Conversion between the two systems is relatively simple. One nanometer is equal to ten Angströms.
The abbreviation A or A.U. remains an important historical term in gemology. It reflects the scientific methods used in gemstone analysis. Knowledge of this unit helps readers understand older publications. It also provides insight into the development of gemological science. For these reasons, the term continues to appear in gemstone literature.

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SHELL

Shell made of calcium carbonate, shells show a wide range of sizes and colours, from the iridescent colours of pearl oyster shells (Pinctada maxima and Pinctada margaritifera), blue-green iridescence of abalone, paua (the type of abalone that is found in the waters around New Zealand) and topshells (trochidae), to the delicate white and pink layers of the conch shell.

In addition to marine shells, a wide range of river and terrestrial shells is also used as beads and in jewellery, particularly if they show a colourful iridescence.

Occurrence

Shells are found worldwide. Conch is found in the Bahamas (where conch fritters are a favourite food), Madagascar and the Maldive Islands. Abalone molluscs are found off the coast of South Africa and the USA.

Maori people have a long tradition of gathering paua for its meat, as well as using the shell in their carvings and as a Taonga (the Maori word for treasure). Paua has become the shell associated with gifts from New Zealand.

Mother-of-pearl cabochons, mosaic pieces for inlay, or as decorative pieces. Some shells have an iridescent coating of mother-of-pearl. Mother-of-pearl is made of nacre, the same material that coats a pearl. Nacre is usually a pale colour, though the nacre lining the shells of Tahiti can be dark.

Where the layer is thick enough, mother-of-pearl can be fashioned as beads, spheres or domed cabochons, but mostly thin layers are used, for example, as low relief decorative pieces.

Shells that have layers of different colours may be fashioned as cameos. The outer layer is cut away to reveal an inner layer of a different colour. Examples include the pink and white of the conch, and the spider conch (Lambis lambis), the mottled cream and brown of the tiger cowrie (Cipraea tigres) with the violet inner layer, and the white outer layer of shells (including Cassidae madagascarensii), which have an inner layer of beige or brown.

Cameos

Tortoiseshell

Tortoiseshell was made by warming and flattening the shell of the Hawksbill turtle and was used to produce, for example, tortoiseshell cases, hair combs and brooches. However, since 1973 this turtle has been an endangered species and the sale of tortoiseshell has been banned.

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