Oil-Shale
cess
T h i s research wa5 undertaken by the Bureau of \lines t o procure the chemical, phjsical, and engineering data necessary for extracting oil from oil shale and refining shale oil into products meeting commercial specifications. The data are essential for the development of appropriate processes and for the design, construction, and operation of commercial plants. Under this research program, basic information is being developed on the composition and characteristics of Colorado oil shale and its shale oil. Engineering and process data are also being made available for converting these materials into acceptable motor fuels and useful by-products, These results are t h e basis for the future development of a new industrj for preparing liquid fuels and allied products from a n extensibe, b u t hithertofore unused natural resource-oil shale. This industr? will aid the national economy by increasing the reserve of petroleumlilce matei*iials. Shale oil, however, diRers considerably from petroleum, and difierent retiniiig techniques must he clebised and utilized to process shale oil into acceptable pr0duct.i.
officc v a s established on the campius of the Lniversit,y of JYyoini11.r through a cooperative agreement bctneen the University and the B U ~ W of L I Miiies to aid in developing petroleum resources of tlio st,ate. Itesearch investigatione pert,ained to the production of erude oils of the Rocky Xountain region, especially Kyoming. The einphasia on production studies continued until 1930, wheu studies were started on utilization of high sulfur, asphalt-hearing crudo oils commonly known as "black oils.'' The field office operated until 1933. In 1935, R petroleum experiment st,ation was established in cooperation with the University of JTyoming. S i n e years later, Laramie was also considered a logical location for research on oil shale: and in 1936 the Peti~oleumand Oil-Phlc: Xxperiment Station n-as established. l>E23C:RIP'I'IO\ OE' >EW S T 4 I T 0 1
The nevi building was caompleted in the spring of 104;' at a n initial cost of 8550,000 on land donatcd by thr I-niversitv of ITyorning adjacent to its campus. =\t the present time, the at>&-
Apparatus for Petroleum and Crude Shale Oil Analyses by Bureau of Rlines Routine IkIethod Unit in background gives direct comparison of prebsure distillations inade in laboratories at high altitudes and distillations made at sea level
SDEIZ the Synthetic Liquid Fuels A4ctof' 1944, oil-shale research and process development hj, the Bureau of Mines are centralized in a new building of the Petroleum and Oil-Shalc Experiment Station at Laramie, Wyo. Sowhere else in the world is research on oil shale conduct,ed on such an. extensive basis. This oil-shale research is correlated closely with the demonstration mining and processing of oil shale a t Rifle, Colo. At Laramie, experimental work is performed to obtain basic technical data essential for a future oil-shale indust,ry. This includes process development and t,he determination of engineering data necessary for the design, construction, and operation of large pilot or demonstration plants for producing oil from shale and refining the oil into products of commercial quality. Analyses are made of foreign oil shales and their products. Hen-ever, most of the experimental work is done on oil shales of the Green River formation; large deposits occur in Colorado, Utah, and \l-yoniing. Oil-shale research represents a relatively recent expansion of the activities at, the Laramie station. In 1924. a pet,roleurn field
Unit Consisting of Eight Modified Fischer Retorts for Assay of Oil Shale Oil :iclds of 11,500 samples h a \ e been determined
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January 1951
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tion, including equipment and supplies, represents an investment for analysis; equipment for calibrating field instruments and anaof about $1,000,000. The building has a floor space of approxilyzing core and bottom-hole samples obtained in oil and gas mately 50,000 square feet. The central section of the structure reservoir studies; assay and petrographic equipment for the is four stories high with two wings; one of the wings is one story analysis of oil shale; catalyst evaluation units; test engines high, and the other is three stories high. The building has a for determining the octane and cetane ratings of motor reinforced-concrete frame with a natural sandstone facing that fuels; high efficiency distillation and silica gel adsorption harmonizes with the dominant architectural style of the buildings columns for hydrocarbon analyses; and miscellaneous instruments, such as an x-ray diffraction machine, refractometers, on the campus. I n accordance with modern construction practice, the building infrared and ultraviolet spectrometers, polarograph, and mass is designed functionally for efficiency and safety. A split heating spectrometer (the only one in use in the Rocky Mountain region). and ventilating system is used. Air to the building is filtered and An engineering laboratory, two stories high, in one wing of the tempered by means of steam coils, then conducted t o the indibuilding, accommodates equipment for engineering studies of oil vidual rooms where supplementary heat controlled thermostatishale and shale oil. For the most part, these units are constructed cally is added by steam radiators. Only the air from the offices for continuous operation on a large bench scale or semipilot and halls is recirculated. Fumes from the laboratories are explant scale. Included are units for retorting oil shale by various cluded from the remainder of the building by venting the air methods and for determining its thermal characteristics, also from the laboratories directly to the outside. Stairways are equipment for fractionating, hydrogenating, and cracking shale located in the center and at each end of the building. Fire hoses, oil by different refining processes. portable fire extinguishers, and safety showers are located in the PERSONNEL corridors; a first-aid room is on the main floor. The staff of the station consists of 100 technical and 35 nonThe main building contains 33 laboratories with offices, shops, technical employees, including chemists, engineers, petrographers, garage, heating plant, and auxiliary facilities. These include scientific aides, draftsmen, custodians, clerks, stenographers, and storage space for equipment and supplies including dry oil-shale skilled workmen as mechanics, machinists, electricians, and instrusamples, flammable oils and solvents, and hot and cold rooms for ment makers. Several science students a t the University of the storage or handling of special samples. Some facilities are Wyoming are employed on a part-time basis. Twenty-five located in several structures adjoining the new building. Administechnical employees are engaged in projects pertaining t o petrotrative offices provide for maintenance of the building and the leum, and the remaining 75 are engaged in oil-shale and shale-oil handling of correspondence, purchases, files, personnel actions, projects. and similar functions. A library contains documents and pubPETROLEUM RESEARCH lished information related particularly to petroleum and oil shale Petroleum research was conducted by the Bureau of Mines for including bound and current periodicals, reference books, reapproximately 19 years in the former petroleum field office and prints, microfilms, and patents. Drafting and photographic petroleum experiment station and is coneauioment and facilities for reoroducina tinued in the present station. illustrations by photostating and black Petroleum Production. Engineering and white printing are available. A studies are being made t o promote the garage is provided for the storage and best recovery of oil and gas from fields in maintenance of cars and trucks, and well the Rocky Mountain region. Included equipped machine, instrument, electrical, are detailed studies of reservoirs and resglass, and wood-working shops are used for maintenance and, particularly, for the ervoir conditions and the procurement of engineering data which are pertinent construction of special experimental to the production of oil by primary equipment. and secondary recovery methods ( 1 1 ) . Most of the individual laboratories are designed t o accommodate one t o four Basic d a t a on oil and gas fields are being people who are working on the same or collected to aid in the industrial developrelated projects. Each laboratory is fully ment of the region. I n this regard, a equipped with steel furniture. T h e recent survey revealed that a reserve of over 6,500,000 tons of sulfur is benches have stone tops and outlets for available b y processing hydrogen sulfide hot and rold water, electricity, gas, compressed air, and vacuum. Additional outfrom some of the above fields (10). lets for steam and electrical power are Petroleum Chemistry and R e h i n g . Most of the crude oils in the region have available in each room and a tap for distilled water is located on each floor. been compared and analyzed by the BuAll laboratories have fire extinguishers, reau of Mines routine method ( 2 , 3 ) . and many contain fume hoods with indiOther studies include determination of vidual blowers to exhaust air directly outnitrogen in crude oil (4). Many Rocky Mountain crude oils also have a high asside the building. Standard laboratory equipment is phalt and sulfur content. The yields and available for determining the basic properties of the asphalts are being studchemical, physical, and engineering data ied (95). Working in cooperation with involved in the production and processing the American Petroleum Institute through of petroleum, for producing oil from oil Research Project 48, the fundamental shale, and for converting shale oil into properties of sulfur compounds which marketable products. Extensive special may be useful in identification procedures equipment is also available. This inare being determined. As a literature cludes a field laboratory for measuring High Efficiency Fractionating Colstudy failed to orovide adeauate - (lk, . limns for Separating Petrdeum the pressure and temperature conditions information, sulfur compounds are being and Shale Oil into Narrow-Boiling in oil and gas wells with depths to 18,000 purified for determination of physical Fractions at Atmosnheric or Refeet and for taking bottom-hole samples duced P r e s k r e properties and for use as standards. Some
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 1
tains large quantities of unsaturated hydrocarbons and hetelocyclic compounds. Therefore, the initial step in determining the composition of shale oil is the use of reliable methods of analysis. Methods for hydrocarbon determinations by f ractional distil la ti or^ and silica gel adsorption (6, 8 , 9),direct determination of oxygen, determinat'ion of nitrogen (,2Y), determination of nitrogen compounds, spectroscopic identification of individual compounriu, and the separation of sulfur xrid nitrogen compounds by atlsorption are being investigated. Composition studies h a w been reported (1) on a ixaphtha from shale oil, and work is now proceeding on highcr boiling frai:tions. Considerable work is done on the Separation (22) arid identification ( 1 7 ) of compounds of sulfur, nitrogen, and oxygc:~~. These compounds are responsible, t'o a considerable: extent, for the difficulties encouritcwtl in shale-oil processing. Sitrugen compounds are particularly troublesome and are prcs(>nt i r i great,er quantities in oils from Green River oil ehale t h m i n oils from foreign oil shales thiit liuvc1 heen analyzed to datcx. Oil-Shale Retorting. On the unproved assumption that tlestrurtive distillation is the best or most practical means of producing oil from oil shale, the engineering studies are chiefly C O I I cerned with determining: Catalyst Evaluation Unit and Apparatus ( L e f t ) for Study of Catalytic Cracking of Organic Nitrogen Cornpounds
sulfur compounds are also being subjected t o thermal cracking to determine thermal stabilities and reaction mechanisms. This information will be used t o devise more effective methods for removiug wlfur from the high sulfur crude oils. OIL-SHALE AND SHALE-OIL RESEARCH
The basic objectives of this workare the development of procesJes and the procurement of chemical, physical, and engineering data necessary for the design, construction, and operation of plants for producing oil from oil shale and for refining shale oil into marketable products. Five general types of research are involved:
1. Analysis of oil shale 2 . Analysis of shale oil 3 . Engineering and processing studies for retorting oil shale 4. Engineering and processing studies for refining shale oil 8. Development of useful by-products Oil-Shale Analysis. Analytical research is conducted to obtain basic information of thc compositions and characteristics of oil shales from differentdeposits to det,ermine t8heieasibility of using these materials as a source of oil. Some foreign oil shalcs which have been utilized commercially are analyzed. However, most of the resea,rch pertains to oil shales of the Green River formation (16,27)" To date, about. 11,500 assays were made to determine the oil yields of oil-shale samples derived principally from exposed deposits, diamond-drill test holes, and oil and gas wells. These data are used in determining the extent and richness of oil-shale deposits. Detailed studies of oil shales include determinaion of physical properties and chemical composition (15, 14). In mttny instances, standard analytical methods are not applicable to oil shale. Accordingly, ari important part of this program is the development of more reliable assay and analytical methods (19, 2 4 ) . Studies are also in progress to determine the chemical constitution and properties of the organic material in oil shale, which is converted to shale oil by heating (16). This organic material is not a compound but a mixture of many complex compounds. However, it is surprisingly uniform in oil shale from a particular deposit. Identification of the major organic constituents is being investigated by analyses of the organic materid and it,s degradation products (20). Shale-Oil Analysis. Shale oil, like petroleum, is composed of hydrocarbons and constituents w sulfur, nitrogen, and oxygen derivatives of hydrocarbons. Unlike petroleum, however, I t con-
1. Thermal requirements for retorting oil shalt. 2. Rate of heat transfer to beds of oil shale 3. Effect of oxygen in retortinggas on the quantit,y and quality of oil 4. Effect of variations of retorting conditions as tcmpcrature, pressure, time, shale particle size, and retorting atmosphtw on the quantity and quality of oil ( 2 1 , 26, 27')~
These studies show that little heat is actually consumed in converting organic material to oil; moet' of the applied heaL is recoverable as sensible heat in the spent shale and retorting products (M). The effect of rctorting variables is being detcrmined in a bench scale, continuous screw-feed, externally heated retort designed for operation over a wide range of experimental conditions. In a bench-scale experimental retort, which utilizes radiant heat, the organic material in finely divided oil shale is rapidly converted to oil (20). At temperatures of 1200' t o 1800O F., the conversion requires only a fraction of a second to yield highly aromatic oil. Also under investigation is a thermal solution process by which the organic material in oil shale is converted to oil and gas by heating a slurry of pulverized shale and shale oil under pressure (19). With hydrogen pressure of 4000 pounds per square inch, complete conversion of organic material has been attained (20). The advantages of the thermal solution process are greater yields of oil and gas and improved heat transfer rates. However, equipment prohlems of handling the slurry have not been solved.
Three-Tube Combustion Furnace for Macrodetermination of Carbon and Hydrogen in Organic Materials
January 1951
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Shale-Oil Refining. These studies include compilation of basic engineering data necessary for the refining of shale oil and the development of new refining and processing methods. As the composition of shale oil differs from that of petroleum, particularly with respect to the amounts and types of hydrocarbons and its content of compounds of nitrogen, sulfur, and oxygen, a considerable portion of the work is concerned with application and adaptation of petroleum-refining methods to shale oil and application of processes which are not commonly used on petroleum (6, 19, 26). Studies are in progress to determine the optimum conditions for the thermal and catalytic cracking of shale oil and the effect of these conditions on the yield and quality of the products (18). In general, shale-oil fractions are characterized by poor stability 111 that they darken rapidly on standing and have a high gum content ( 7 ) . These changes are attributed partsly t o nitrogen compounds-particularly pyrroles, The naphthas have low octane numbers and poor tetraethyllead susceptibility but good sensitivity. The heavier fractions contain considerable wax and asphalt. Other processing methods (20) under study include hydrogenation, a t pressures as low as 500 to 1500 pounds per square inch, by which a wide range of shale-oil fractions can be converted to stable products having a low content of nitrogen and sulfur compounds. Solvent extraction also appears to be a promising method of preparing special products as Diesel fuel and feed stocks for further processing. For example, a solventextracted feed stock, representing approximately 50% of a gas oil, yielded essentially the same amount of naphtha by catalytic cracking as was obtained by the catalytic cracking of the entire gas oil. I n addition, the naphtha from the solvent-extracted stock showed improved stability and lower nitrogen and sulfur content. As there is a lack of information in the literature, studies are in progress to determine the effect of different types of nitrogen compounds on refining operations and on the performance of finished shale products. Included are studies of the reactions of nitrogen compounds by thermal and catalytic cracking and the effect of these compounds on different catalysts. Experimental results also indicate that under certain conditions the presence of nitrogen compounds in shale-oil products may be beneficial. For example, the octane numbers determined by the motor method of pyridine and alkylated pyridine are in excess of 100 and may possibly be used to improve the octane rating of gasoline. Oil-Shale and Shale-Oil By-products. Studies are in progress to develop useful secondary or by-products which will utilize completely the oil shale and its products and in some instances avoid disposal problems. On the basis of quantity, the major byproduct is spent shale from retorting. Experimental results to date show that the spent shale from Green River oil shale consists primarily of calcite and dolomite, clay, quartz, feldspar, plagioclase, a carbonaceous residue (resembling fixed carbon), and small amounts of many minor elements (13). None of these materials appears to be of sufficient value to warrant recovery a t the present time. The more promising by-products are those obtained by refining or treating shale oil. Heavy gas-oil distillate, the counterpart of petroleum wax-distillate, yields a considerable amount of crude wax by solvent extraction (38). Treating this crude wax with acid and clay yields a fully refined paraffin wax which is comparable to that obtained from petroleum and also a mixed parafiolefin wax and a wax consisting principally of olefins. A wax of high melting point can be separated from the distillatisn residue of heavy gas oil. Tar acids and bases are recoverable in considerable quantity from shale oil $0). The tar acids consist predominantly of phenol homologs with some carboxylic acids from which phenolics of low molecular weight have been prepared. The extensive commercial uses for tar acids offer an attractive market for these materials from shale oil. Tar bases consisting of homologs Of pyridine and pyrrole are available in greater quantities froin
19
Radiant Retort for Producing Highly Aromatic Oil from Oil Shale Oil-shale retention time is only a fraction of a second at temperatures of 1200' t o 1800" F.
shale oil than are the tar acids. Commercial uses for these tar bases are being investigated. Viscous, asphaltic residues are also obtained from crude shale oil (26). Experimental studies show that road oils and asphalts of different consistencies can be prepared by the distillation, cracking, solvent extraction, or air blowing of shale oil. These residue8 resemble petroleum asphalts to a considerable extent and may be used for some of the same purposes. There is also a possibility that the shale-oil residues may be suitable for the m'anufacture of special a$phalts. LITERATURE CITED
(1) Ball, John S., Dinneen, G. U., Smith, J. R., Bailey, C. W., arid
Van Meter, Robin, IND.ENG.CHEM.,41. 581-7 (1949). (2) Ball, John S., and Espach, Ralph H., Petroleum Eng., 19, N o . 13, 229-34 (1948). (3) Ball, John S., Wenger., W. J., and Whisman, hZ. L., Petroleum Processing, 5, 842-6 (1950). (4) Ball, John S., Whisman, M. L., and Wenger, W. .J., presented before the Division of Petroleum Chemistry, 118th Meeting AMERICAN CHEMICAL SOCIETY, Chicago, Ill. ( 5 ) Barnet, W. I., U . S. Bur. Mine8 Inform. Circ. 7516 (1949). (6) Dinneen, G. U., Bailey, C. W. Smith, J. R., andBall, J o h n s . , Anal. Chem., 19,992-8 (1947). (7) Dinneen. C. U., and Bickel, JT7. D., pvesented before the Division of Petroleum Chemistry, 118th Meeting AMERICAN CHEMICAL SOCIETY, Chicago, Ill. (8)Dinneen, G. U., Smith, 5. R., and Ball, John S., Petroleum Ref i t ~29, ~ , NO. 5 , 129-34 (1950). (9) Dinneen, G. U., Thompson, C . J., Smith, J. R., and Ball, John S., Anal. Chem., 22, 871-6 (1950). (IO) Esprtch, Ralph H., IND.ENG.CHEM.,42, 2235 (1950). (11) Espach, Ralph H., and Nichols, H. Dale, U . S. Bur. Mines Bull. 418 (1941). (12) Frost. I. C., and Stanfield, K. E., Anal. Chem., 22, 491-2 (1950). (13) Frost, I. C., Stanfield, K. E., McAuley, W. S., and Smith, H. N., presented before the Division of Gas and Fuel Chemiatry, 118th SOCIETY, Chicago, Ill. Meeting AMERICANCREMICAL
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INDUSTRIAL AND ENGINEERING CHEMISTRY
(14) Heady, Howard H., thesis submitted to University of Wyoming in partial fulfillment of requirements for degree of Master of Science (1948). (15) Helm, R. Vernon, Haines, William E., and Ball, John S.,U . S. Bur. Mines R e p t . Invest. 4566 (1949). (16) Hubbard, Arnold B., and Robinson, IT-. E., Ibid., in press. (17) Janssen, Arthur G., thesis submitted to University of Wyoming in partial fulfillment of requirements for Ph.D. degree 11950). (18) Murphy, W. I. R., Tihen, S. S.,and Cottingham, P. L., presented before Division of Petroleum Chemistry, 115th Meeting ARIEIZICAKCHEXICAL SOCIETY, San Francisco, Calif. (19) Secretary of the Interior, L'. S . Bur. M C n e s Rept. Invest. 4457 (1949). 1 2 0 ) Ihid.. 4562 (1950). (21) Sham,,R. J., 4151 (1947). 2 2 ) Smith. J. R., Smith, C. R., Jr., and Dinneen, G . U., AMII C h e m . , 22,867-70 (1960). \ -
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IT.,Mitchell, L. E., Cox, R . J . , Barnet, W.I., and Murphy, W.I. R., IND. ETG.CHEM.,43, 33 (1951). (24) Stanfield, K. E., and Frost, I. C., U . S . Bur. Mines R e p t . I n u e s t . 3977 (1946); 4477 (1949). (25) Stanfield, K. E., and Hubbard, Rethe!, L., V . S. Bur. Mines Tech. Paper 717 (1949). (26) Thorne, H. M., Murphy, TT. I. R., Ball, J. S., Shnfield, K. E.. and Horne, J. IT.,IND. ENG.CHEM.,43, 20 (1951). (27) Thorne, H. M., Murphy, TI-.I. R., Stanfield, K. E., Ball, J. S., and Horne, J. K., presented before the Institute of Petroleum, Second Oil-Sha!e and Cannel Coal Conference, Glasgow, Scotland (1950). ( 2 8 ) Tisot, P. K., and Horne, Joseph IT., C,S.Bur. M i n e s R e p t . I m e s i . 4708 (1950). (29) T'an Meter, R. A , Neel, J. C., Brodie, E. C., and Ball, J. S.. presented before the Division of Petroleum Chemistry, 115th SOCIETY, San Francisco, Calif. Meeting AMERICANCHEMICIL RECEIVED September 23, 1950. (23) Sohns, H.
haracteristics and Utilizatio
Oil Shale and Shale H. M. THORNE, W. I. R . MURPHY. J. S. BALL, K. E. STANFIELD, AND J. W. HORNE C . S . Bureau of Mines, Laramie, W y o .
T
T h i s paper presents a general discussion of the properare determined by s t a i i t l d ties and characteristics of oil shales, shale oils, and their applies to a variety of analytical methods. In ~ o m e products, and presents briefly the results of major phases instances, t h e s e 8 t a n d a r d fine-grained s e d i m e n t a r y of the research and process development work now in methods are not entirely allrocks containing organic progress at the Laramie, Wyo., station of the Bureau of material which is only slightly plicable to oil shales, which Mines. For the most part, the experimental work pertains commonly contain both orsoluble in petroleum solvents to oil shale of the Green River formation in Colorado. The ganic and inorganic materials but is largely converted to properties of products obtained by retorting the oil shale in widely different amounts. oil by the application of heat. and refining its shale oil by several different processes are Bccordingly, improved anaAccording to one theory, oil given. The properties of Green River oil shale and its lytical methods are requircd, shale was formed in quiet products are also compared with those determined for particularly for determining lakes or seas by simultfineous several foreign oil shales. the quantity and ultimate deposition of mineral and composition of the organic organic matter in situ. This material in oil shale. This organic m a t t e r c o n s i s t e d organic material consists chiefly of compounds of carbon, hyof small plants such as algae, pollen, and spores, or a strucdrogen, oxygen, nitrogen, and sulfur-elements t'hat also occur t,ureless jelly or sapropel derived from the plants as a result of in the inorganic portion of the shale. Some of the properbacterial action. Green River oil shale, particularly the rich oil ties of Colorado (Green River) and several ot,her oil shales shale, is a tough rock rather than a typical shale, and it is someare shown in Table I. These particular samples contained aptimes referred to as marlstone. proximately 18 to 55% organic mat'erial. The total sulfur and The Colorado oil shales are from the Green River formation total nitrogen contents ranged from 0.4 to 1.7% and 0.4 to 0.9yo, and represent various grades of shale currently being mined and respectively, whereas the carbon to hydrogen ratios of organic processed into shale oil and refined products a t the Bureau of materials ranged from 6.3 to 11.1. The organic material Mines oil-shale demonshation mine and plant near Rifle, Colo. with the highest carbon to hydrogen ratio yielded the least oil. The importance and extent of the Gret.n River formation were This trend is further shown in Table 11, where the data are given recently described by Belser (5). He estimated that an area of for shales in the order of increasing richness. In general, the 16,500 square miles exists in adjoining portions of Colorado, Utah, richest shales from a given source showed the maximum converand Wyoming and t,hat the portion of this formation assaying sion of available organic material to oil. These and other data more than 15 gallons of oil per ton of shale contains 300 billion indicated that the efficiency of the conversion to oil by the aseag barrels of oil. retorting procedure was dependent on the character of the orExtensive physical and chemical propc\rties of Colorado oil ganic material and, to a lesser extent, on the amount and charshales are given b s Frost et al. (11). These show the oil shales of acter of the associated mineral matter in the shale. the Green River formation to be highly laminated sedimentary Table I11 shows the composition of ashes from several shales. rocks ranging in color from gray for a lean shale to dark brown These data, together with petrographic and x-ray diffraction for a rich shale. Chemical and petrographic examination of analyses, showed that the types and amounts of the mineral conthe Green River shales showed them to be composed essent.ially stituents varied greatly. The mineral portion of the Colorado of calcite, dolomite, clay, and yellow organic nlaterial; the minor shale consist.ed predominantly of calcite or dolomite, clay, quart,z, constituents are quartz, orthoclase, andesine, pyrite, marcasite, plagioclase, and feldspar; in the Australian ehale the mineral n-as analcite, opal, black organic material, and small woody fragchiefly quartz; and in the South African and Brazilian shalee the ments. mineral was principally clay. The Spanish shale was not, esOil shales are commonly compared according to their oil yields amined petrographically or by x-ray diffraction, but its mineral is by the modified Fischer retort method (19), and t,heir properties
HE term "oil shale"
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