Abstract

Santaclaraite, ideally CaMn4[Si5O14(OH)](OH) · H2O, occurs as pink and tan veins and masses in Franciscan chert in the Diablo Range, Santa Clara and Stanislaus Counties, Calif. It is associated with four unidentified Mn silicates, Mn-howieite, quartz, braunite, calcite, rhodochrosite, kutnohorite, barite, harmotome, chalcopyrite, and native copper. Santaclaraite is triclinic, space group B1, a = 15.633(1), b = 7.603(1), c = 12.003(1)Å, α = 109.71(1)°, β = 88.61(1)°, γ = 99.95(1)°, V = 1322.0(3)Å3, Z = 4. The strongest lines of the X-ray powder pattern are (d, I, hkl): 7.04Å, 100,010; 3.003, 84, 501; 3.152, 80,410; 7.69, 63, 200; 3.847, 57, (113,400); 3.524, 39, 020. Crystals are lamellar to prismatic (flattened on {100}), with good cleavage on {100} and {010}; H = 6½; D(calc.) = 3.398 g/cm3, D(meas.) = 3.31(±0.01); optically biaxial negative, with α = 1.681, β; = 1.696, γ = 1.708 (all ±0.002), 2VX = 83 (±1)°. Although chemically a hydrated rhodonite, santaclaraite dehydrates to Mn-bustamite at about 550°C (in air). Santaclaraite is a five-tetrahedral-repeat single-chain silicate and has structural affinities with rhodonite, nambulite, marsturite, babingtonite, and inesite.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.