Opal

opal

(ō`pəl), a mineral consisting of poorly crystalline to amorphous silica, SiO₂·nH₂O; the water content is quite variable but usually ranges from 3% to 10%. Common opal is usually colorless or white, but it may be gray, brown, yellow, or red; the color is due to fine-grained impurities. Opal is formed at low temperatures from silica-bearing waters and can occur in fissures and cavities of any rock type. Precious, or gem, opal has a rich iridescence and remarkable play of changing colors, usually in red, green, and blue. This is the result of a specific internal structure consisting of regularly packed uniform spheres of amorphous silica a few tenths of a micron in diameter; sphere diameter and refractive index determine the range of colors displayed. The greater part of the world's supply of precious opal comes from the Coober Pedy and Andamooka fields in South Australia. The original source, known in Roman times, was in what is now E Slovakia. Precious opal has also been mined in Honduras, Mexico, and the Virgin Valley in Nevada. Fire opal is a bright red transparent or translucent opal that may or may not show a play of color.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Opal

 

a mineral; a compact natural hydrogel with composition SiO₂·nH₂ O. It occurs mainly as aggregates of extremely fine grains of low-temperature cristobalite. Most opal contains 2–14 percent H₂O; the usual admixtures include MgO, CaO, Al₂O₃, and Fe₂O₃.

Opal forms stalactitic, lamellar, or porous masses. Its hardness on Mohs’ scale is 5.0–6.5; its density is 1,800–2,250 kg/m³. The color varies, depending on the impurity content (white, yellow, brown); colorless varieties are also known. Translucent varieties are typically iridescent. The more common varieties include hyalite, which is colorless and clear; precious opal, with an attractive play of colors; and hydrophane, a porous semitranslucent opal. Certain rocks are composed entirely of opal—for example, geyserite, diatomite, and tripolite.

The formation of opal is associated with deposition of silica from hot volcanogenic waters or with decomposition of silica under the action of water and carbonic acid in the zone of weathering. The skeletons of diatoms and radiolarians form opal of biogenic origin. Colored iridescent opals are used as decorative stones; precious opal is a gemstone. Opal deposits in the USSR are found in the Ukraine and Kazakhstan, and abroad, in Hungary, Czechoslovakia, Mexico, and Australia. Among the opaline rocks, diatomites and tripolites have the greatest practical importance.

G. P. BARSANOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

opal

[′ō·pəl]

(mineralogy)

A natural hydrated form of silica; it is amorphous, usually occurs in botryoidal or stalactic masses, has a hardness of 5-6 on Mohs scale, and specific gravity is 1.9-2.2.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

opal

A hydrous form of silica containing 2 to 10% combined water; reacts with cement alkalies and may be highly detrimental as an aggregate in concrete.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

opal

October. [Am. Gem Symbolism: Kunz, 319–320]

See: Birthstones

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opal

unlucky stone; represents the Evil Eye. [Gem Symbolism: Kunz, 148, 320]

See: Luck, Bad

Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.

opal

an amorphous, usually iridescent, mineral that can be of almost any colour, found in igneous rocks and around hot springs. It is used as a gemstone. Composition: hydrated silica. Formula: SiO₂.nH₂O

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Opal

(1)

A DSP language.

["OPAL: A High Level Language and Environment for DSP boards on PC", J.P. Schwartz et al, Proc ICASSP-89, 1989].

Opal

(2)

The language of the object-oriented database GemStone.

["Making Smalltalk a Database System", G. Copeland et al, Proc SIGMOD'84, ACM 1984, pp.316- 325].

Opal

(3)

A simulation language with provision for stochastic variables. An extension of Autostat.

["C-E-I-R OPAL", D. Pilling, Internal Report, C.E.I.R. Ltd. (1963)].

Opal

(4)

A language for compiler testing said to be used internally by DEC.

Opal

(5)

A functional programming language designed at the Technische Universitaet Berlin as a testbed for the development of functional programs. OPAL integrates concepts from Algebraic Specification and Functional Programming, which favour the (formal) development of (large) production-quality software written in a purely functional style.

The core of OPAL is a strongly typed, higher-order, strict applicative language which belongs to the tradition of Hope and ML. The algebraic flavour of OPAL is visible in the syntactical appearance and in the preference of parameterisation to polymorphism.

OPAL supports: information hiding - each language unit is divided into an interface (signature) and an implementation part; selective import; parameterised modules; free constructor views on sorts, which allow pattern-based function definitions despite quite different implementations; full overloading of names; puristic scheme language with no built-in data types (except Booleans and denotations).

OPAL and its predecessor OPAL-0 have been used for some time at the Technische Universitaet Berlin in CS courses and for research into optimising compilers for applicative languages. The OPAL compiler itself is writte entirely in OPAL.

An overview is given in "OPAL: Design And Implementation of an Algebraic Programming Language".

http://cs.tu-berlin.de/~opal/.

ftp://ftp.cs.tu-berlin.de/pub/local/uebb/papers/DesignImplOpal.ps.gz.

This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)

Opal

The original name of software from CA Technologies that converts legacy output from mainframes and minicomputers into a graphical-based format. Now part of its Advantage Integration Server suite, the technology provides the development environment and supports 3270, 5250 and VT220 terminals and ODBC-compliant databases. Development can be done by drag and drop or by scripting in OpalScript or VBScript. A Telnet connection to the mainframe is provided and maintains a connection to the desktop allowing the Web browser or a Windows client with the software to have access to the newly formatted data. See green screen.

From Green Screen to the Web

Advantage Integration Server (formerly Opal) transforms legacy applications (top) into graphics-based documents (bottom) that can be accessed via a Web browser or Windows client software. (Screen examples courtesy of CA Technologies, Inc.)

From Green Screen to the Web

Advantage Integration Server (formerly Opal) transforms legacy applications (top) into graphics-based documents (bottom) that can be accessed via a Web browser or Windows client software. (Screen examples courtesy of CA Technologies, Inc.)

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