SOIL Particles That Glitter Are Often Mistaken for Gold

All is not gold that glitters; but we hesitate to take the chance of missing anything valuable, especially anything as valuable as gold. Therefore, when we see something that glitters we naturally want to investigate. One of the results of this very human tendency is that every year a large number of soil samples are received by the Bureau of Chemistry and Soils with the request that the bright, shiny particles in the soil be identified.  Obviously the writers believe the particles to be gold. Often they say so. But unfortunately there are a great number of substances which glitter, many of them not even metals.

In soils perhaps mica and pyrite are the commonest and most deceptive of all these glittering substances. Both are found in numerous rocks, such as granites, schists, and gneisses; and in certain of these rocks, such as mica schists, the mica may be the most abundant mineral present. When these rocks are exposed for long ages to the action of the atmosphere they decompose or rot and form soils.  During this process the oxygen and moisture of the air act upon the pyrite chemically and so change it that usually nothing visible is left except iron rust. But the mica continues to persist. In spite of all the time that has elapsed since the parent rock started to decompose, the mica can still be seen glittering in the soil about as brightly as ever. Owing to its flaky structure, it can be transported by water and wind more readily than can most other soil minerals and is therefore found in many soils which originated from rocks devoid of mica.  In fact there are very few soils in which no mica can be found.

It is not gold; but neither is it altogether useless. Although it decomposes extremely slowly, yet it does decompose and yields a little potash to the soil. But even in this respect it may be deceptive, for it may still glitter after practically all of its potash has disappeared.