Annual production of cement in California is as follows: Reference: State Mineralogist Reports IV, XII. Bulletin 38. Chromic iron ore, to the extent of 1,517 short tons, valued at $9,434, was produced during 1914.* While the material is known to exist in many places in the State, and has been mined in several other counties, including Fresno and Glenn, the present production comes entirely from Calaveras and Shasta counties, with a small amount from Tuolumne. The European war caused some rise in the price of this material, as most of the chrome used in the United States is imported from Rhodesia and New Caledonia. Considerable effort, therefore, was expended by private parties in investigating California deposits, more particularly with the idea of expecting to find large quantities which would justify entering the market and making long-time contracts, in competition with the foreign deposits. Most of these investigations were without success, as the California deposits are in most cases, not beyond the prospective stage. There is no reason why the industry should not see a considerable growth, however, in the future. *These figures are from signed returns of the actual producers, which we have verified and find correct, though at variance with the data available to the U. S. Geological Survey as indicated in their Mineral Resources, 1913. The annual output of chromite since 1887 is as follows: Distribution by counties is shown in the following table: Magnesite. Reference: State Mineralogist Reports XII, XIII. Bulletin 38. Magnesite has for a number of years been known to exist in many localities in California. In quality it is very high grade, many deposits yielding material carrying about 95% magnesium carbonate. The deposits are mostly in the metamorphic rocks of the Coast Range and Sierra Nevada Mountains, and are scattered over an area nearly four hundred miles long. One deposit of sedimentary origin is situated in the Mojave Desert region. During the year 1914 there was considerable activity in the production of magnesite, giving a larger output than during any previous year except 1910. Doubtless the curtailing of some European supplies, due to the war, and the added possibilities for transportation through the Panama Canal, to eastern markets, have led to the increased production. The permanent nature of improvements at some deposits gives promise that future production will be still greater. The following concerns are among those producing in 1914: Cedar Mountain Magnesite Mine, Alameda County, where the rock was mined by the glory-hole system, and calcined in a flat hearth furnace, using oil fuel and having a daily capacity of about ten tons of crude. The Sherlock Mine, Santa Clara County, quarries the rock and ships it in the crude state. At the Red Mountain deposit, the material is stoped underground, calcined in a vertical shaft kiln, and transported 33 miles by auto trucks to the railroad. The Sonoma Magnesite Company, Sonoma County, is installing rotary kilns and a short railroad for delivery to the main line. The Tulare Mining Company, Tulare County, stopes the magnesite exposed in underground workings, and calcines the product. A number of owners have carried on development work, and it seems assured that a much greater demand can easily be met by the various California deposits. The principal uses at the present time include: refractory linings for basic open-hearth steel furnaces, copper reverberatories and converters, bullion and other metallurgical furnaces; in the manufacture of paper from wood pulp; and in structural work, for flooring, wainscoting, tiling, sanitary kitchen and hospital finishing, etc. In connection with building work it has proven particularly efficient as a flooring for steel railroad coaches, on account of having greater elasticity and resilience than "Portland" cement. For refractory purposes, the magnesite is "dead-burned"-i e., all or practically all of the CO, is expelled from it. For cement purposes, it is left "caustic"i. e., from 5% to 10% of CO is retained. When dry caustic magnesite is mixed with a solution of magnesium chloride (MgCl2) 2 * * * in proper proportions, a very strong cement is produced, known as oxychloride or Sorel cement.* "It is applied in a plastic form, which sets in a few hours as a tough, seamless surface. It has also a very strong bonding power, and will hold firmly to wood, metal, or concrete as a base. It may be finished with a very smooth even surface, which will take a good wax or oil polish. As ordinarily mixed there is added a certain proportion of wood flour, cork, asbestos, or other filler, thereby adding to the elastic properties of the finished product." Its surface is described as "warm' and "quiet" as a result of the elastic and nonconducting character of the composite material. The cement is usually colored by the addition of some mineral pigment to the materials before mixing as cement. The desirable qualities of any flooring material (cost not considered) are listed for purposes of analysis or comparison under eighteen heads, as follows: Cleanliness (sanitary qualities), quietness, immunity from abrasion (surface wear), resilience, immunity from slipperiness, appearance, waterproof waterproof character, plasticity, warmth (thermal insulation), life (immunity from deterioration with age), acid-proof character, alkali-proof character, fire resistance, elasticity, crushing strength, structural strength (rupture), immunity from expansion and contraction, and lightness. The importance of these several qualities varies with the varying requirements to be met; for instance, in some places, as in hospitals, cleanliness is one of the prime considerations; in other places immunity from abrasion might be one of the principal requisites. As to most of these qualities the conclusion is reached that the magnesia cement affords one of the most satisfactory flooring materials for many purposes such as in kitchen, laundry, toilet, and bathrooms, corridors, large rooms or halls in public or other buildings, including hospitals, factories, shops and restaurants. There is no doubt that the material is steadily coming into more general recognition and favor for these uses. For a few special uses it is more or less disqualified; as an instance, it is not suited for construction of swimming tanks or for conditions of permanent wetness, since under constant immersion it gradually softens, although it is said to withstand intermittent wetting and drying and is recommended for shower baths. Naturally it is not acid-proof and not wholly alkali-proof, which might be a disadvantage in use for laboratory floors and tables; but these are rather special requirements. Its cost per square foot is given as 25 to 33 cents, depending on area, which is estimated to be lower than marble, cork, rubber, clay or *In this summary of the uses and properties of magnesia cement we have drawn freely from the following references: Eng. Soc. Western Pennsylvania Proc., 1913, vol. 29, pp. 305-338, 418-444; mosaic tile, slate, or terrazzo, although more expensive than wood, asphalt, linoleum, or Portland cement. In the discussion of the subject the causes of failure are ascribed to uncertain climatic changes, lack of uniformity in the mixtures used, lack of care on the part of those handling the materials, possible deterioration of materials used through exposure (either before or after mixing), lack of proper preparation of foundations on which the material is to be laid, and, as a very important factor, experience or nonexperience in the manipulation or actual laying and troweling of the material. Data concerning the percentages of magnesium chloride and of ground calcined magnesia and data concerning the character and quantity of filler and color added to the commercial preparations are naturally guarded as trade secrets by the firms already in the business. The examination and standardization of the raw materials used, and of acceptable filler materials, and the establishment of standard proportions for the mixtures would seem to be about the only satisfactory way of attacking the problem. The condition of the calcination of magnesite for cement uses is important, as the same material may undoubtedly be very greatly varied in its reacting properties by differing treatment in the kiln. It is generally agreed that the magnesite for cement use must be comparatively free from lime, as lime has a greater tendency to reabsorb water and carbon dioxide than the magnesia, thereby causing swelling, and is therefore not so permanent in the completed cement as a pure magnesia material. The fillers used may constitute 10% to 40% of the whole cement, and commonly consist of ground marble, sand, sawdust, cork, asbestos, or other materials. As an example of the formulas used in mixing such cements the following are quoted:* Mixtures for the underlying or coarser layer. *Scherer, Robert, Der Magnesit, sein Vorkommen, seine Gewinnung und technische Verwertung, pp. 216-217, A. Hartleben's Bibliothek, Wien und Leipzig 1908. |