Barite Crystal Development

Barite Crystal Development


At the Monroeville locality, barite has a unique morphology, which often causes the crystals to have a mix of vitreous and crude faces. Discounting the fact that some crystals of barite have been heavily corroded from exposure to the elements of the river, many of the fresher crystals on the inside of septaria have certain naturally rough faces.

These rough, rounded, etched or feathered faces make the task of identifying additional modifications nearly impossible. A very few sporadic crystals without distorted faces have also been observed but are not as common.

The crude faces are generally an indication of the rate at which the crystals formed, and furthermore that some faces likely grew too quickly to fully develop. While the basal pinacoid, macrodome, brachydome and macropinacoid faces are usually sharp with a glass-like polish, other faces like the unit prism and brachypinacoid faces are more often rough and uneven.

Occasionally the macropinacoid will also be rough as well as any additional macrodome faces. A typical example of this phenomenon is displayed in the photo to the left. Notice how the unit prism has unique stress mark edges as if this face was stretched away from the surrounding sharper faces.

The center of this face is smooth, but does not have the glass like polish found on many other faces of this crystal. This is very characteristic of the unit prism faces and may indicate that the unit prism formed slightly too fast. The macropinacoid and brachypinacoid are often much rougher, almost to the point of being unidentifiable.

These faces likely developed at an even faster rate. Another example of this development can be seen in the crystal in the photo to the lower left. This crystal has 3 sets of macrodome faces. Notice that the main macrodome is sharp and the succeeding macrodome faces are increasingly crude.

This effect is often amplified in very large crystals, causing the macropinacoid and/or brachypinacoid to have feathered faces. Crystals larger than 2 centimeters in size are also more opaque with multiple growth faces and are less distinct than crystals of smaller size. An example of this is pictured to the lower right Larger crystals are of the same form as the small isolated crystals, but are merely elongate along the Y axis of the crystal.

Smaller crystals are typically water clear with well defined faces and unique crystalline shaped bubble inclusions. These are viewable inside the crystal in the photo to the lower left. Most barite will have these inclusions, but smaller crystals tend to display this characteristic best.

Physical Properties of Massive Barite

In addition to the difference in color and clarity, large crystalline masses of barite from the septaria have a few other unique characteristics, rarely observed among small isolated crystals. First, while these masses are often

created by multigrowth parallel or bifurcated crystals that over grew the pockets, smaller crystals tend to be singular individuals. Second, the larger crystals and masses are often opaque with patches of pale yellow, purple, gray and rarely blue color.

The specimen in the photo to the left is an example of pale purple massive crystalline barite. Large masses occasionally show a medium salmon red fluorescence under short wave ultraviolet light as displayed in the photo to the right. The fluorescent yellow mineral is massive ferroan dolomite.

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