The symbol for the element aluminum.

[ahl] An Italian word meaning "at the," "to the" or "on the." For example, al dente means "to the tooth."

For more information on al-, visit Britannica.com.

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Al
Hexagonal -- scalenohedral

Environment

Common in crystals in plutonic, pegmatitic, and metamorphic rocks, and in placer accumulations.

Crystal description

Six-sided crystals, sometimes elongated into barrels, tapering bipyramids, or sharp flat-topped prisms, but also in thin 6-sided plates. Massive metamorphic occurrences have large embedded crystals, showing series of parallel striations, like the plagioclase feldspars. May be in fine-grained pepperlike disseminations with magnetite (emery).

Physical properties

Colorless, brown, black, yellow, red, blue, violet. Luster adamantine; hardness 9; specific gravity 3.9-4.1; fracture conchoidal or uneven; cleavage none, but has well-developed partings on rhombohedral planes and sometimes on the base. Breaks into sharp fragments (brittle), but often is very tough; transparent to translucent; often triboluminescent, and fluorescent orange, yellow, or red.

Composition

Aluminum oxide (52.9% Al, 47.1% O).

Tests

Infusible and insoluble.

Distinguishing characteristics

When opaque and nondescript in form and hue, it is poorly crystallized and resembles many silicate minerals. The fine parallel rulings on parting faces are distinctive and might result in a confusion with some feldspars. It often shows color bands and bronzy luster on basal planes. The great hardness is diagnostic; since it is harder than any other natural mineral except diamond, a hardness test should suffice. Good crystal form and high specific gravity (higher than in most silicates) are also distinctive, when they can be observed or determined. Gemmy crystals, those of ruby and sapphire, are simpler.

Occurrence

Usually characteristic of rocks deficient in silicon oxide, with which presumably the aluminum oxide would otherwise combine to form another mineral. Found in igneous rocks, particularly with nepheline, as an accessory. Also found in pegmatites, in basalt dikes, in schists formed in regional metamorphism of sediments accompanied by an introduction of solutions of aluminum oxide, and in metamorphosed limestones. Associated with spinel, kyanite, garnet, and high-calcium feldspars.

Corundum was long an important industrial abrasive and refractory, but also has many gem varieties. The collector's emphasis will be on gemmy crystals for which there are numerous localities, so only a few of the important ones can be mentioned. The gem gravels of Sri Lanka (Ceylon), perhaps formed from weathered pegmatites, perhaps from solution-eaten marbles, are rich in gemmy corundum. Blocks and crystals of corundum have been mined in Africa, Brazil, and Madagascar for abrasive uses. Some of the South African crystals are particularly well formed and may be very large. The rubies and sapphires of Myanmar (Burma) occur as crystals in a metamorphosed limestone, and many are recovered as residual remnants in the earth resting on top of the fresh rock. Tanzania, along the Umba River, is becoming an important source, where the corundum crystals occur in vermiculite (hydrated mica) dikes and as red plates (ruby) in green zoisite (Longido Hills).

The U.S. occurrences are as large crystals and masses in Georgia and North Carolina, together with a few rubies and sapphires. In Montana it is found near Helena in waterworn pebbles in terrace gravel bars by the Missouri River and at Yogo Gulch as flat, blue, gemmy crystals in a dark-colored fine-grained igneous dike. In California small but well-formed crystals have been found in Riverside, San Bernardino, and San Diego counties. Emery (corundum with magnetite) has been mined at Peekskill, New York, and Chester, Massachusetts.

Remarks

The gem colors are caused by minor metal oxide impurities. Ruby, for example, is colored by chromium oxide. Corundum is often fluorescent, glowing red or orange in ultraviolet light, and some is strongly triboluminescent, giving orange flashes when it is sawed or hammered.

Corundum has proved easy to synthesize (except that temperatures near 2000°C are required), crystallizing instantly on the solidification of the molten aluminum oxide. This has led to the mass production of synthetic jewelry stones by simple melting of a suitably pigmented powder in an oxyhydrogen flame and allowing the hot rain to build up a stalagmite, known as a boule, which is then cut up into decorative stones. Invented by a French chemist in 1891 who claimed to reconstruct rubies, it is known now as the Verneuil process. Lately, ruby crystals have been grown by hydrothermal methods, crystallized from molten solutions, and "pulled" as rods from pots of fused aluminum oxide, for use as bearings, gems, and lasers.

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Chemical symbol, aluminum.

Dansk (Danish)
symb. - aluminium

abbr. - Alabama

Français (French)
symb. - (Chim, symb) aldéhyde

abbr. - Alabama

Deutsch (German)
symb. - (Chem.) Aluminium

abbr. - Alabama, anglo-lateinisch

Ελληνική (Greek)
abbr. - αλουμίνιο

Español (Spanish)
symb. - símbolo químico del Aluminio

abbr. - Alabama, anglo-latín, American League (una de las dos ligas profesionales de béisbol en Estados Unidos), American Legion (asociación de veteranos de las fuerzas armadas norteamericanas)

Svenska (Swedish)
abbr. - Alabama

中文（简体） (Chinese (Simplified))
美国联盟, 美国军团, 美国退伍军人协会

铝

中文（繁體） (Chinese (Traditional))
abbr. - 美國聯盟, 美國軍團, 美國退伍軍人協會

symb. - 鋁

한국어 (Korean)
symb. - aluminium(알루미늄)

abbr. - American League(미국 직업 야구 연맹)

العربيه (Arabic)
‏(اختصار) مختصر معناه ألتعلم من خلال ألأداء‏

עברית (Hebrew)
symb. - ‮אלומיניום (יסוד), אנגלו-לטיני‬
abbr. - ‮אנגלו-לטיני, הלגיון האמריקאי, הליגה האמריקאית (בכדור-בסיס)‬

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Al 1631	zone al
al 1641	al martino