What is your favorite mineral? Mine is a brave isometric mineral called Franklinite. Franklinite is in the spinel group with many other minerals that have a cubic or isometric crystal system. The spinel group, specifically the iron spinel group, consists of minerals such as magnetite, which is commonly used in steel production, and zinc ferrite, which is used as a pigment. Like the name of the subgroup, all minerals in the iron spinel group contain the element Fe, or iron. But unlike the other minerals, franklinite was the one that caught my attention the most.

Franklinite was discovered in 1819 in Franklin, New Jersey and was named for the place where it was found and for America’s inventor, Benjamin Franklin. Mentioned above, franklinite is a mineral of the iron spinel group and has an isometric crystal system. The mineral itself is a metamorphic rock and has a hardness of 5.5 to 6. Although the chemical formula of pure franklinite is (Zn,Fe2+)(Fe3+)2O4, franklinite is usually found with manganese, which makes it the formula more recognizable: (Zn,Mn2+ ,Fe2+)(Fe3+,Mn3+)2O4.

Here’s a fun fact: Franklinite used to be a major zinc ore during the time the Franklin and Sterling Hill mines were open. The mines eventually closed, the use of franklinite in zinc disappeared, and it ceased to be an important mineral in zinc production. However, the ore is still an important ore of iron, hence the reason for its name in the subgroup.

Color is what most attracts people’s attention. The color of franklinite varies mainly from black to gray with frequent appearances of white. Although difficult to notice in some photos, franklinite has veins that are reddish-brown to black in color and fragments that are known to be translucent. There are also times when different minerals would interlock with Franklinite. But in most cases, the mineral would be zinc, which looks red and blotchy.

You may be wondering why an opaque colored mineral like franklinite caught my eye, but I personally find dark, metallic colors to be the most appealing to my eyes. It was not only the color, but also the octahedral shape of the mineral itself. I found the shape of the mineral fascinating and the fact that it fluoresces under UV light. Much like granite or marble, the mineral’s dark colors show the strata of the rock and the patterns and lines that appear from the layers to create interesting indentations and contours. There are also times when the mineral looks like graphite and looks like you can draw or write with it. All of these facts make something that may seem boring at first glance interesting and aesthetically beautiful.