Fluorite and Barite (#28)

Matte, banded, gemmy dark emerald green modified cubes of fluorite to 2" maximum dimension, studded with scattered elongate dull white translucent barites to 1 ¾" in length.
Africa Okarusu, Namibia 12" x 6 ¼" x 5"

 

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If you are working your way through this display numerically, then you have seen fluorite already, but not barite. If you are not, you may have seen neither. The chemical formula of fluorite is CaF2, and that of barite is BaSo4. There are several things about the two that are very different, but the most striking difference would not be evident from this specimen. If you were to pick up a specimen of fluorite all by itself and then one of barite by itself, you would immediately be struck by how heavy the barite felt. In this specimen, you would of course feel the weight of both combined.

The Periodic Table of the Elements is a graphical display of all of the natural elements, as well as man-made elements synthesized thus far. Each element has an "atomic number," which is the number of protons in its nucleus, and the table is arranged by increasing atomic number. The natural elements run from atomic number 1 (hydrogen) to number 92 (uranium). Each element also has an "atomic weight," which is the weight of the atom compared to the weight of an atom of the most common isotope of carbon. If that sounds a bit technical, don't worry about it - just know that in general, atomic weight increases with atomic number.

The atomic numbers of Ca and F are 20 and 9, respectively. Ba, S, and O are numbers 56, 16, and 8. So it should not come as a surprise that barite would feel heavier than fluorite. We call this "relative heaviness" density. It is measured as mass per unit volume - usually in the metric system in scientific work, such as grams per cubic centimeter (g/cm3). The density of fluorite is 3.2 g/cm3, and that of barite is 4.5 g/cm3. Most minerals that make up the bulk of rocks on earth have densities in the range of 2.6-3.3 g/cm3, so barite would feel distinctly heavy.