72 GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
cement is surpassed among mineral products only by iron, coal, and oil; in rate of increase 
in annual production during the last decade even these three products can not be compared 
with it. In 1890 the total production of Portland cement in the United States was 335,500 
barrels, valued at $439,050; in 1903 it exceeded 22,000,000 barrels, while the value was over 
$27,000,000. 
CEMENT MATERIALS IN GENERAL. 
In view of the importance of this industry, the occurrence of large deposits of good cement 
materials in Mississippi is a matter of great interest to the citizens of the State. The raw 
materials used in the manufacture of Portland cement are limestones and clays, both of 
which are found in satisfactory quality and quantity in several different parts of Mississippi. 
ESSENTIAL CONDITIONS. 
Portland cement is produced by burning a finely ground artificial mixture consisting 
essentially of lime, silica, alumina, and iron oxide, in certain definite proportions. Usually 
this combination is made by mixing limestone or marl with clay or shale, in which case about 
three times as much of the lime carbonate should be present in the mixture as of the clayey 
materials. The burning takes place at a high temperature, approaching 3,000° F., and 
must therefore be carried on in kilns of special design and lining. During the burning, com- 
bination of tlif lime with silica, alumina, and iron oxide takes place. The product of the 
burning is a semifused mass called clinker, and consists of silicates, aluminates, and ferrites 
of lime in certain definite proportions. This clinker must be finely ground. After such 
grinding the resulting powder is Portland cement. 
The finished product is blue to gray in color, has a specific gravity of 3 to 3.25, and when 
mixed with water will harden or set. 
The product must be uniform in composition and quality; and as the processes of manu- 
facture involve certain chemical as well as physical changes, four points may be regarded 
as of cardinal importance in making Portland cement. These are: 
1. The cement mixture must be of the proper chemical and physical composition. 
2. The raw materials of which it is composed must be finely ground and intimately mixed 
before burning. 
3. The binning must be conducted at the proper temperature. 
4. After burning, the resulting clinker must be finely ground. 
The methods of manufacture of Portland cement have been recently described in some 
detail by the present writer in several reports which are still readily obtainable. Reference 
should therefore be made to the reports mentioned a m case information in regard to manu- 
facturing details is desired. In the present report only such matters as directly concern the 
question of raw materials will be discussed. 
For the purposes of the present report it will be sufficiently accurate to consider that a Port- 
land cement mixture, when ready for burning, will consist of about 75 per cent of lime car- 
bonate (CaC0 3 ) and 20 per cent of silica (Si0 2 ), alumina (Al 2 3 ), and iron oxide (Fc 2 3 ) 
together, the remaining 5 percent including any magnesium carbonate, sulphur, and alkalies 
that may be present. 
The essential elements which enter into this mixture — lime, silica, alumina, and iron — are 
all abundantly and widely distributed in nature, occurring in different forms in many kinds 
of rocks. It can therefore be readily seen that, theoretically, a satisfactory Portland cement 
mixture could be prepared by combining, in an almost indefinite number of ways and propor- 
tions, many possible raw materials. Obviously, too, we might expect to find perfect grada- 
tions in the artificialness of the mixture, varying from the one extreme, where a natural rock 
of absolutely correct composition was used, to the other extreme, where two or more mate- 
rials, in nearly equal amounts, are required to make a mixture of correct composition. 
a Discussions of the materials and method of Portland cement manufacture are contained in the follow- 
ing three publications, all of which are distributed free of charge and may be obtained on application to 
the proper officials: 
1. Senate Doc. No. 19, 58th Cong., 1st sess., 1903. 
2. Bulletin Mo. 8, Alabama Geol. Survey, 1904. 
3. Bulletin No. 243, U. S. Geol. Survey, 1905. 
