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The lattice parameters of natural spinel, ferroan gahnite, magnesiochromite, and synthetic spinel at elevated temperatures have been determined. The results are: spinel at = 8.0870 + 35.24 x 10-6t+ 45.73 x 10-gt 2, 22 < t< 840°C; ferroan gahnite at = 8.1050+ 54.35 x 10-6t+ 10.53 x 10-9t 2, 22< t< 845°C; magnesiochromite at = 8.2965 + 56"82 x 10-6t+ 8"08 x 10-9t 2, 22 < t < 823 °C, synthetic spinel at = 8.0821 +45.79 x 10-6t+35.69 x 10-9t 2, 26< t< 800°C, where at is the lattice parameter in ~ at t°C. Expressions for thermal expansions are derived. The replacement of magnesium cations by zinc and iron and of A1203 by Cr203 in spinel decreases the mean thermal expansion in the range of temperatures covered, but increases the lattice parameters.

Dredge samples and photographs from the Blake Plateau, off the southeast coast of the United States, indicate that a layer of manganese oxide forms pavement that may be continuous over an area af about 5000 square kilometers. The manganese pavement grades into round manganese nodules to the south and east and into phosphate nodules to the west. The Gulf Stream probably maintains a very unusual environment that prohibits deposition of clastic sediment and permits accretion of manganese pavements.