Excerpts from Jim Conrad's
Naturalist Newsletter

from the September 21, 2007 Newsletter issued from Sierra Gorda Biosphere Reserve, QUERÉTARO, MÉXICO

At midday I was looking for shade so when I saw an abandoned adobe hut across the valley I followed burro and goat trails toward it, the actual road to it long severed in several places by landslides and washouts.

The structure was roofless and at midday the sun was so directly overhead that the building afforded hardly any shade at all. A cluster of mesquites rose nearby so I headed there and found that they hid the entrance to an old mine. Gold, silver... ? I tried to remember my old geology-class thinking patterns. The mine was exactly where two geological formations met, one side of the shaft being against limestone, the other against darker, crumbly rocks I couldn't identify. Then I saw it, the red streak across white limestone shown below:

mercury in rock

The only mineral I could remember with that dark, blood-red color is cinnabar, a mineral composed of equal numbers of atoms of mercury and sulfur, as shown by its chemical formula HgS. I'd heard of mercury mines in these mountains, and here was one of them.

To confirm my suspicion I examined the shattered rock tailings pushed into the valley below the mine and there I found many rocks coated with the same bloody color, and a few pebbles of apparently pure cinnabar. You can see a rock from the tailings below:

mercury in rock

Long ago people learned how to separate mercury from rocks like these by crushing and then heating them until the mercury evaporated, the fumes being distilled almost like alcohol. Since mercury is a metal that is liquid at room temperature it's not surprising that it evaporates at a relatively low heat. You might enjoy reading about mercury, which is quite a remarkable element, and a dangerous one, too, at http://en.wikipedia.org/wiki/Mercury_(element).

Near the abandoned mine stood the claim marker claiming rights to all land within 300 meters. It's shown below:

marker at old mercury mine in Mexico