Caminite: a new magnesium-hydroxide-sulfate-hydrate mineral found in a submarine hydrothermal deposit, East Pacific Rise, 21/sup 0/N

Journal Article · · Am. Mineral.; (United States)

OSTI ID:7146411

Maymon, R M; Kastner, M

As laboratory experiments predict, a Mg-hydroxide-sulfate-hydrate mineral, here named caminite, precipitates in nature from seawater heated in an active submarine hydrothermal system. Caminite is found intergrown with anhydrite in the wall of a black-smoker chimney precipitated around hydrothermal fluids discharging on the East Pacific Rise axis at 21/sup 0/N latitude. Caminite is tetragonal with a = 5.239 A and c = 12.988. Bond-strength calculations and experimental results predict that the caminite structure accommodates a range of compositions described by a general formula: MgSO/sub 4/ x Mg(OH)/sub 7/ (1 - 2x)H/sub 2/O, where 0 less than or equal to x less than or equal to 0.5. The caminite in the authors sample has a composition corresponding to a stoichiometry of MgSO/sub 4/ 0.4Mg(OH)/sub 2/ 0.2H/sub 2/O. It is soft (H = 2.5) and apparently colorless. Caminite is uniaxial negative and has low birefringence (0.002). Its indices of refraction are omega = 1.534 and epsilon = 1.532. In the recharge zones of submarine hydrothermal systems, large volumes of convecting seawater headed above approximately 240C may precipitate abundant caminite and anhydrite. Formation of abundant caminite can drastically lower the pH of downwelling seawater in such systems, and rapid removal of sulfate into caminite and anhydrite may prevent the reduction of much seawater sulfate to sulfide within the hydrothermal system. Incorporation of seawater sulfate into caminite and anhydrite at elevated temperatures and subsequent recycling of this sulfate into the oceans by dissolution at low temperatures should affect the oxygen-isotope composition of seawater sulfate and may play a part in maintaining the oxygen-isotope values of oceanic sulfate in disequilibrium with /sub 0//sup 18/O of seawater.

• Research Organization: Univ. of California, Santa Barbara
• OSTI ID: 7146411
• Journal Information: Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 71:5-6; ISSN AMMIA
• Country of Publication: United States
• Language: English

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