THE TRICLINIC SYSTEM

The lack of symmetry gives rise to the thought that the triclinic system is the closest system to amorphism, having no form or order. It is actually the other way around. Triclinic minerals have a more sophisticated ordering of the atoms in their structure than other minerals. Ordering is a way of saying that the atoms are precisely placed into specific sites and these sites, in the case of triclinic minerals, are not symmetrically arranged.

As an analogy think of an alphabetic filing system with lots of random, unsorted papers scattered among the files. A scattering of unsorted papers might produce a more or less even distribution of papers among the files and in turn form a more-or-less symmetrical distribution, at least to the size of each file. In other words, the A file has just as much chance to have say 10 papers in it as the B file or C file, etc. But if the papers are sorted alphabeticly, the distribution of papers is now irregular or asymmetrical, because files like A might contain a lot of papers and files like Q, hardly any.

This kind of ordering occurs in mineral structures where various positions for atoms are assigned to specific elements. The more specific the site and the more specific the element that occupies those sites then the less symmetrical, but more ordered, the structure.

MICROCLINE

• Class: 2nd
• Symmetry: Bar 1
• Symmetry Elements: Only a center
• Crystallographic Axes: three axes of three different lengths
• Angles: None equal to 90 degrees.
• Common Forms: The Pinacoid is the only form although various pinacoids are classified as 1st, 2nd, 3rd and 4th order pinacoids, as well as front, side and basal pinacoids.
• Most Common Minerals: Albite, amblygonite, anapaite, andesine, anorthite, anothoclase, astrophyllite, axinite, babingtonite, baumhauerite, bustamite, bytownite, ceruleite, chabazite-(Ca), chalcanthite, chalcosiderite, chloritoid (triclinic), collinsite, copiapite, cornubite, cuprosklodowskite, cylindrite, diadochite, emmonsite, fairfieldite, ferroaxinite, fiedlerite, fluckite, frankeite, gageite-1tc, gordonite, halloysite, hydrodresserite, inesite, jamesite, kermesite, kyanite, labradorite, lengenbachite, ludlockite, manganaxinite, manganbabingtonite, metakottingite, microcline, miserite, montebrasite, nambulite, nealite, oligoclase, paradamite, paravauxite, pectolite, picropharmacolite, planerite, pyrophyllite, pyroxmangite, rhodonite, sapphirine, serandite, serendibite, serpentine, strunzite, symplesite, tarbuttite, tinzenite, turquoise, ulexite, ussingite, vauxite, weloganite and wollastonite. The Pinacoidal Class is fairly large with over 250 recognized minerals belonging to this class.

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MURMANITE

• Class: 1st
• Symmetry: 1
• Symmetry Elements: None
• Crystallographic Axes: three axes of three different lengths
• Angles: None equal to 90 degrees.
• Common Forms: Only the Pedion.
• Most Common Minerals: Amesite, donnayite-(Y), epistilbite, epistolite, hilgardite, kaolinite, leucophanite, magnesio-axinite, murmanite, nacaphite, nefedovite, tundrite and tyretskite. The Pedial Class contains roughly 50 known members.

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