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GEOREF RECORD

Formation of natural gypsum megacrystals in Naica, Mexico

Juan Manuel Garcia-Ruiz, Roberto Villasuso, Carlos Ayora, Angels Canals and Fermin Otalora
Formation of natural gypsum megacrystals in Naica, Mexico
Geology (Boulder) (April 2007) 35 (4): 327-330

Abstract

Exploration in the Naica mine (Chihuahua, Mexico) recently unveiled several caves containing giant, faceted, and transparent single crystals of gypsum (CaSO (sub 4) .2H (sub 2) O) as long as 11 m. These large crystals form at very low supersaturation. The problem is to explain how proper geochemical conditions can be sustained for a long time without large fluctuations that would trigger substantial nucleation. Fluid inclusion analyses show that the crystals grew from low-salinity solutions at a temperature of approximately 54 degrees C, slightly below the one at which the solubility of anhydrite equals that of gypsum. Sulfur and oxygen isotopic compositions of gypsum crystals are compatible with growth from solutions resulting from dissolution of anhydrite previously precipitated during late hydrothermal mineralization, suggesting that these megacrystals formed by a self-feeding mechanism driven by a solution-mediated, anhydrite-gypsum phase transition. Nucleation kinetics calculations based on laboratory data show that this mechanism can account for the formation of these giant crystals, yet only when operating within the very narrow range of temperature identified by our fluid inclusion study. These singular conditions create a mineral wonderland, a site of scientific interest, and an extraordinary phenomenon worthy of preservation.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 35
Serial Issue: 4
Title: Formation of natural gypsum megacrystals in Naica, Mexico
Affiliation: Universidad de Granada, Instituto Andaluz de Ciencias de la Tierra, Granada, Spain
Pages: 327-330
Published: 200704
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 23
Accession Number: 2007-037419
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2007080
Illustration Description: illus. incl. sect.
N25°45'00" - N32°00'00", W108°00'00" - W103°00'00"
Secondary Affiliation: Compania Penoles, MEX, MexicoCSIC, ESP, SpainUniversitat de Barcelona, ESP, Spain
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200720
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