| Popis: |
MAX (mineralogical analysis by x-ray diffraction) is an interactive computer program for teaching identification of clay minerals based on standard x-ray diffraction characteristics. The program also illustrates the principles of identification of nonphyllosilicates. The program consists of tutorial-type exercises for identification of 16 standard clay minerals, mixtures of two or more of the standards that can be used for self-testing, diffractograms of 28 soil clay mienrals from several continents and countries, and a small section on identification of nonclay minerals. MAX can easily be run by the novice computer user. It is used to supplement lectures on soil mineralogy and can be used to replace portions of the traditional laboratories in clay mineralogy courses. IDENTIFICATION of clay minerals by diffraction x-ray techniques is an essential part of soil mineralogy. Correct interpretation of diffractograms allows even the novice mineralogist to make inferences about the chemical and physical characteristics of the soil that can be useful for various practical applications. This interpretation skill is not often taught, especially at the undergraduate level, and diffraction patterns retain an aura of mystery and complexity to the uninitiated. Additionally, it is becoming more and more difficult to include a hands-on laboratory approach in clay mineralogy courses as costs of diffractometer operation and maintenance exceed dwindling university budgets. MAX was originally introduced into the soil mineralogy program at the University of Alberta in 1986. It is used to complement the lectures and laboratory portion of the program by developing the skill of x-ray diffractogram interpretation. This skill is normally developed only by people who work extensively in the mineralogical field and is gained through considerable experience. MAX allows the student to gain this expertise by examining the diffraction characteristics of standard clay minerals and then testing their knowledge by identifying unknown clay minerals. The students work at their own pace, with as much repetition as they feel is required for acquiring the necessary identification skills. Interpretation of clay mineral diffractograms is essentially selftaught using MAX, and is integrated with more theoretical material in the lectures. Every time MAX is used, a record is kept of the time and date, and of everything that the student does in the program, such as which standard minerals are examined or the test score which they obtained for the unknown mixtures. This gives the inDepartment of Soil Science, Earth Sciences Bldg., Univ. of Alberta, Edmonton, AB T6G 2E3 Canada. Received 21 Jan. 1993. *Corresponding author. Published in J. Nat. Resour. Life Sci. Educ. 22:169-172 (1993). structors an indication of usage, of where problems and successes are occurring, and identifies areas instructors may supplement during lectures. CLAY SAMPLE PREPARATION The program MAX accesses a database of more than 700 clay mineral diffractograms. Standard clay minerals were obtained from Ward’s Natural Science Establishment, Inc., Rochester, NY, with the exception of the chloritic intergrade standard, which was obtained from a representative soil. Soil samples were collected from various areas of the world. Samples were dispersed in distilled water by ultrasonic vibration (Genrich and Bremner, 1972), and the clay-size fraction (< 0.002 mm) was separated using gravity sedimentation techniques (Jackson, 1979). Subsamples of the clay-size fraction were saturated with Ca2÷ and K + by repeated treatments with 1 mol L ~ solutions of the respective chloride salts followed by washing with distilled water to remove excess electrolyte. Oriented specimens for x-ray diffraction analysis were prepared on glass slides using the paste method (Thiesen |
Plný text