No abstract

Extensive deposits of kaolinite in Florida are formed by transformation of montmorillonite during low-temperature supergene weathering. The transformation occurs by intracrystalline leaching of interlayer cations and tetrahedral silica layers. Interposition of stripped layers within montmorillonite creates a regular 1:1 mixedlayered montmorillonite-kaolinite, a new clay structure. Kaolin-like layers are nourished by lateral epitaxy, as the iron-rich montmorillonite decomposes. Hexagonal outgrowths of new kaolinite develop at the edges of montmorillonite flakes and nucleate new vertical growth. Kaolinitic sands impregnated with goethite are ultimately formed, and the released silica enriches groundwater and forms secondary chert.

Pecoraite is a new phase in the natural system H(2)O-NiO-MgOSiO(2), the nickel analog of clinochrysotile. It occurs in cracks in the Wolf Creek meteorite in Australia where it was formed under hydrothermal conditions. Particles of pecoraite are very small curved plates which have begun to coil; some have achieved spiral form.

TABLE 3. Spectrographic analyses (in percent) of four merumite samples _ 9 4. X-ray powder patterns of merumite (eskolaite 37 percent, guyanaite 63 percent), merumite approaching eskolaite (Guyana), guyanaite (Guyana, four strongest lines), eskolaite (Finland), and Cr2O8 9 5. Cell constants of guyanaite (from Guyana and Finland), and of CrOOH, ScOOH, and InOOH 11 6. Analyses of guyanaite ______________________-_ __________ ______________ ____ _____ _ 12 7. X-ray powder data of (Cr, Al, Fe, Ti, Mn)02 from guyanaite, and CrO2 from CrOOH _ 8. X-ray powder data of (Cr, Al, Fe, Ti Mn) 2O8 ____-_ _ 9. X-ray powder data of guyanaite (from Guyana and Finland), "merumite" and synthetic guyanaite CrOOH 10. Analysis of merumite containing 70 percent bracewellite and 30 percent eskolaite ______ _____ __ _ 11. Spectrographic analysis of merumite containing 70 percent bracewellite and 30 percent eskolaite _ ______ 12. Electron-probe analysis (in percent) of seven crystals of bracewellite and two merumite fragments ______ 13. X-ray powder data for bracewellite, goethite, and eskolaite ___________ __ __ __ __ _ ___ 14. Chemical analysis of grimaldiite-mcconnellite polycrystals _______ _________________ ____ __ ___ 18 15. Microspectrographic analysis of grimaldiite-mcconnsllite polycrystals _____ __ _ _ __ __ ____ _ 16. X-ray powder pattern of grimaldiite and mcconnellite ___________ __ __ __ __ _ ____ __ 17. Cell constants of grimaldiite, mcconnellite, and related substances ______ ______ __ _____ ___ 18. X-ray powder patterns of 7-CrOOH and lepidocrocite ________ _____________ 19. Cell constants of 7-CrOOH and related compounds ___ __ __ ______ ______________ _ ____ ___ 20. X-ray powder data for chromian gahnite Zn(Al0.7, CrOo.sHOi from Guyana and synthetic spinels ________ 23 21. Gold and silver in six fragments of merumite ___ ____ ____ ____ _ 22. X-ray powder data for topaz _____________________________________ __ 23. Analysis of topaz _________________________________________________ ______ 26 24. Crystallographic relationship of the CrOOH compounds and other metallic hydroxides _____ ______ 27 MERUMITE A COMPLEX ASSEMBLAGE OF CHROMIUM MINERALS FROM GUYANA

Iron-nickel spherules, as much as 0.5 mm in diameter, have been found completely embedded in some philippinites. The spherules consist mainly of kamacite with unidentified pink inclusions. The meteoritic origin of these spherules seems reasonable, suggesting that the tektites containing them were formed by asteroidal or meteoritic impact.