SULFIDE MINERAL SYNTHESIS AS A TEACHING TOOL

Teaching introductory geology to students requires conveying the abstract concept that elements are combined in nature to form minerals. This concept can be grounded for students by the inclusion of a series of simple experiments in mineral synthesis suitable for demonstration or as a laboratory exercise. Evacuated and sealed glass and silica tubes have long been used as reaction vessels in the synthesis of minerals and alloys and they are appropriate for use in the classroom due to the relative simplicity of the techniques involved and low cost of materials. The synthesis of sulfide minerals is particularly useful for demonstrating several aspects of mineralogy and petrology.

Students are introduced to laboratory techniques and the role of experiments in geology during the preparation, running, and examination of run products. Students measure S as well as Fe, Cu, Ni, Bi, or other metals and load the experimental charge into a silica tube that has previously been sealed at one end. The contents of the tube are placed under vacuum and the tube sealed by the professor. The tube is heated either in a furnace or using a standard laboratory flame. Pyrite, pyrrhotite, chalcopyrite, bornite, pentlandite, bismuthinite or other compositions can be formed depending on the experimental charge. After the contents are reacted the tube is cooled and opened. Students examine the run products. In the course of a demonstration the starting materials are consumed, intermediate phases such as liquids may be formed, and run products are crystallized with physical properties measurably different from the initial components. Changes in color, crystal form, density, and magnetism can be observed by students to demonstrate that a change has occurred and the identity of the minerals compared to predictions made based on the weights of starting materials. Additional properties and processes can be demonstrated if experiments are incorporated into a mineralogy curriculum.

This introduces an advanced topic in geology, high-temperature experimentation, to students at an introductory level. The changes are easily observable by the students and reinforce classroom material.