Crystal forms of borate minerals from the Fuka mine, Okayama Prefecture, Japan

AbstractData on the dehydration of pentahydroborite, CaB2O(OH)6·2H2O and nifontovite, Ca3B6O6(OH)12·2H2O from the Fuka mine, Japan are presented. Critical temperatures of the dehydration of the borates were determined by thermogravimetric analysis/differential thermal analysis measurements. The untreated mineral samples and their heating products were investigated by X-ray diffraction and Raman spectroscopy. Upon dehydration, both minerals decompose and undergo amorphization, and at greater temperatures crystallize as an orthorhombic calcium borate, CaB2O4 (Pnca). The dehydration paths of the two minerals are different, with nifontovite showing a greater resistance to decomposition and amorphization than pentahydroborite. Differences in the dehydration processes are related to the residuals of the water content and structural accommodation of the borate polyanion.

Download Full-text

Nifontovite and olshanskyite from Fuka, Okayama Prefecture, Japan

Mineralogical Magazine ◽

10.1180/minmag.1994.058.391.10 ◽

1994 ◽

Vol 58 (391) ◽

pp. 279-284 ◽

Cited By ~ 20

Author(s):

Isao Kusachi ◽

Chiyoko Henmi

Keyword(s):

Hydrothermal Alteration ◽

Chemical Analyses ◽

Calcium Borate ◽

Unit Cell Parameters ◽

X Ray ◽

Cell Parameters ◽

Crystalline Limestone ◽

Wet Chemical ◽

Borate Minerals ◽

Okayama Prefecture

AbstractNifontovite and olshanskyite, two rare hydrous calcium borate minerals, have been found in crystalline limestone near gehlenite-spurrite skarns at Fuka, Okayama Prefecture. Nifontovite occurs as aggregates of tabular crystals up to 5 cm long and 1.5 cm wide, and rarely as euhedral crystals up to 1 mm long. Olshanskyite occurs as anhedral masses, or as micro-twinned platy crystals up to 1 cm long. Wet chemical analyses give the empirical formulae Ca3.052B5.991O6.038(OH)12·1.96H2O and Ca2.888B3.997(OH)18 on the basis of O = 20 for nifontovite and OH=18 for olshanskyite, respectively. The formulae are consistent with those from type localities.The X-ray powder data for these minerals were determined with accuracy. The unit cell parameters of nifontovite agree closely with those published previously. X-ray studies show that olshanskyite is triclinic with the possible space group P1̄ or P1 and a = 9.991(5), b = 14.740(11), c = 7.975(3) Å, α = 94.53(4), β = 69.08(3), γ = 112.44(5)° and Z = 3. The density 2.19 g cm−3 (meas.) obtained for olshanskyite agrees with the estimated ideal value 2.31 g cm−3 (calc.). Nifontovite was formed by hydrothermal alteration of an anhydrous borate, and olshanskyite was formed by hydrothermal alteration of nifontovite and the anhydrous borate.

Download Full-text

The low-resolution 3D-structure of porin, a channel-forming protein in E. coliouter membranes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100075932 ◽

1983 ◽

Vol 41 ◽

pp. 440-441

Author(s):

A. Engel ◽

D.L. Dorset ◽

A. Massalski ◽

J.P. Rosenbusch

Keyword(s):

Crystal Packing ◽

3D Structure ◽

Gram Negative Bacteria ◽

Protein Ratio ◽

Crystal Forms ◽

Large Molecules ◽

Functional Studies ◽

Voltage Dependent ◽

Planar Membranes ◽

Hexagonal Arrays

Porins represent a group of channel forming proteins that facilitate diffusion of small solutes across the outer membrane of Gram-negative bacteria, while excluding large molecules (>650 Da). Planar membranes reconstituted from purified matrix porin (OmpF protein) trimers and phospholipids have allowed quantitative functional studies of the voltage-dependent channels and revealed concerted activation of triplets. Under the same reconstitution conditions but using high protein concentrations porin aggregated to 2D lattices suitable for electron microscopy and image processing. Depending on the lipid-to- protein ratio three different crystal packing arrangements were observed: a large (a = 93 Å) and a small (a = 79 Å) hexagonal and a rectangular (a = 79 Å b = 139 Å) form with p3 symmetry for the hexagonal arrays. In all crystal forms distinct stain filled triplet indentations could be seen and were found to be morphologically identical within a resolution of (22 Å). It is tempting to correlate stain triplets with triple channels, but the proof of this hypothesis requires an analysis of the structure in 3 dimensions.

Download Full-text