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Macromosaic Quartz

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Formula:
SiO2
Prism surface of a macromosaic quartz
Normal habit quartz crystal with macromosaic structure from an alpine-type fissure
Quartz crystals that are composed of slightly tilted and radially arranged wedge-shaped sectors. They can be recognized by the presence of sutures on the crystal faces and the discontinuous striation pattern of the prism faces. This type of quartz has been comprehensively described by Friedlaender in 1951, and hence is also known as "Friedlaender quartz".

Macromosaic quartz crystals are very common, but their surface pattern is often mistaken for a mosaic of twin domains, with the sutures being the twin boundaries. The pattern has nothing to do with twinning, and if twinning is present, the twin domains may form an independent pattern, and twin boundaries will cross the sutures.

Quartz with a macromosaic structure is typical for pegmatites, miarolitic pockets and high-temperature alpine-type fissures. The crystals commonly show a prismatic or tapered habit as well as intermediate forms, and a large variety of accessorial crystallographic forms, in particular the trapezohedron or "x face" { 5 1 -6 1 } and steep rhombohedral faces. Twinning by the Dauphiné Law is common, Brazil Law twinning more rare, and Japan Law twins do apparently not exist.
Macromosaic crystals are commonly twisted slightly around the c-axis, the direction of the twist depends on the handedness of the crystals: Left-handed crystals twist to the right in the direction of growth, whereas right-handed crystals twist to the left (Vollenweider, 1986).
Cross section of a macromosaic quartz in polarized light
Despite their mosaic-like internal structure, cut and polished sections of transparent crystals appear perfectly clear and homogeneous. If a cross section of a crystal is viewed between two crossed polarizers, the internal structure of the crystal becomes visible (see photo to the right).

Macromosaic quartz occurs as rock crystals, smoky quartz or citrine, but not as amethyst. Macromosaic smoky quartz is usually evenly colored.



Classification of Macromosaic Quartz

Chemical Properties of Macromosaic Quartz

Formula:
SiO2
Elements listed in formula:

Occurrences of Macromosaic Quartz

Paragenetic Mode(s):

Other Names for Macromosaic Quartz

Name in Other Languages:

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Macromosaic Quartz

Reference List:
Friedlaender, C. (1951) Untersuchung über die Eignung alpiner Quarze für piezoelektrische Zwecke. Beiträge zur Geologie der Schweiz, Geotechnische Serie, Lieferung 29, 1951.

Vollenweider, P. (1986) Eine überraschende Entdeckung an Quarzkristallen vom Bächistock, UR. Schweizer Strahler: 7: 311-322.

Internet Links for Macromosaic Quartz

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