76 
FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT 
collected clays in Florida that had crystals of selenite (one form of 
gypsum) as much as a half an inch in diameter. 
Rutile —TiCte. This mineral is probably widely distributed in clays, 
usually in small amounts. Few attempts have been made to identify it 
in clays. It rarely occurs in large quantities. Somers 4 reports rutile 
as unidentifiable in three of the one hundred and twelve clays examined 
miroscopically by him, moderate in three, scarce in fifty-three, common 
in twenty, and abundant in thirty-three. Its effect is negligible except in 
white-burning clays. It usually occurs in microscopic grains. 
Ilmenite —TiFe203. It is not definitely known that this mineral 
occurs in clays, but its occurrence is probable in those clays which have 
been derived from soda-rich and basic eruptive rocks. Ilmenite is a 
constituent of some of the sands along the east coast of Florida and its 
presence is to be expected in some of the clays of that region. Its effect 
is perhaps similar to that of rutile. 
Glauconite —This mineral, often called greensand, is a hydrated 
silicate of ferric iron and potassium with aluminum and water in vari¬ 
able proportions, and usually mixed with other minerals. It is easily 
fusible and hence a high percentage of it is not desirable. It is olive to 
grayish-green in color. It occurs in many of the clays of the Atlantic 
coastal plain region and has been reported in clays in New Jersey 1 , 
Maryland 2 , and Georgia 3 4 . 
Chlorite —This term is applied to a group of secondary minerals 
which are hydrous aluminum silicates with ferrous iron and magnesium. 
Ferric iron may sometimes be present. It is found in small quantities 
in some clays. Its presence in the Cretaceous clays of Georgia 4 and the 
Leda clays of Canada 5 has been reported. 
Dolomite —CaMg (COs) 2 . Dolomite is very' similar in composi¬ 
tion and properties to calcite. Alone it is highly refractory, but acts as 
a flux with other minerals. Dolomite is common in some of the clays of 
the Manatee River region. 
4 Somers, R. E., Microscopic Study of Clays, in U. S. Geol. Survey Bull. 708, p. 
292, 1922. 
4 New Jersey Geol. Survey, Final Report, VI, p. 46, 1904. 
2 Maryland Geol. Survey, Eocene, p. 52, 1901. 
3 Veatch, Otto, Clay Deposits of Georgia, Georgia Geol. Survey, Bull. 18, p. 
41, 1909. 
4 Ladd, G. E., American Geologist, Vol. XXIII, p. 240, 1899. 
5 Merrill, G. P., Rocks, Rock Weathering, and Soils, p. 335, 1913. 
