Minerals Day – Earth Science Week 2023

Happy Minerals Day! To celebrate, we are highlighting smithsonite. Smithsonite is a zinc carbonate mineral associated with sphalerite-bearing deposits in north Arkansas and sphalerite-bearing quartz veins in the Ouachita Mountains. The photo above illustrates its yellow color from cadmium and its botryoidal shape or habit. It can also form rhombohedral crystals (see additional photo). Smithsonite and other zinc minerals were important ores in the zinc and lead district of north Arkansas in the late 1800s and early 1900s. Zinc is used to galvanize iron and steel to prevent corrosion and to make brass and alloys for die-casting. Although, we are a net exporter of zinc ores and concentrates, the United States is largely dependent on foreign sources for refined zinc used in manufacturing due to limited smelting capacity. For this reason, zinc was added to the list of critical minerals by the U.S. Geological Survey.

Smithsonite is named in honor of James Smithson, the founder of the Smithsonian Institution.

For more information about critical minerals or other minerals in Arkansas use the link below:

https://www.geology.arkansas.gov/minerals/critical-minerals.html

Geo-pic of the week: Mineralized Vug in Chert

Pictured above is a mineralized vug (approximately 3 inches long) in chert.  A vug is a void or open space in a rock.  Many vugs are filled with minerals after water that is saturated with a certain mineral flows through the rock. This mineralization can happen in multiple stages. The vug above was initially filled with silica-rich fluid therefore quartz precipitated out of solution and lined the walls of the vug.   Afterwards calcite precipitated, as is evident from the larger crystal on the interior left of the vug. 

This vug is present in a section of ornamentally banded chert.  Chert is a sedimentary rock made up of microcrystalline quartz.  It can be a variety of colors or banded and quite beautiful.  The chert above is Devonian age (416-359 million years ago) from northwest Arkansas.