Barite; BaSO4

barite fluorescence

A common misconception among Ohio collectors is that barite is a rare mineral throughout the state. A more accurate statement is that barite is an uncommon mineral at most well known mineral localities in Ohio, with the exception of the Custar Stone company quarry. The reason for this is that many of Ohio’s best known localities are Silurian age dolostones which generally do not produce the mineral. Statewide, barite is frequently observed at Pennsylvanian and Devonian age localities including the Monroeville locality.

However, while barite is one of the more common minerals to occur in septaria at the Monroeville locality, it is perhaps the most difficult mineral to obtain in complete crystal form. This is, in part, due to the tendency of the mineral to develop very large crystals. Bladed barite crystals, typically unterminated, as large as 50 cm have been observed in these septaria. Unfortunately, it is highly unlikely that a large bladed crystal on matrix would ever be collectable as this particular habit of barite is very brittle and unable to withstand the jarring force necessary to split open the septaria.

The typical result of using a sledge hammer to break the tenacious limestone is many small glass-like fragments of larger crystals spilling out of the opened pockets. However, rare smaller but complete crystals of barite are obtainable by the patient collector. The collector, willing to put forth the time and effort necessary to dissect several septaria, stands a fair chance of recovering a small but complete barite crystal. These barite crystals are generally clear with internal feathering and may have vitreous or etched faces. Thicker masses and large crystals may be gray, purple, yellow or rarely blue.

Barite Occurrence

Barite is the second most common mineral, after ferroan dolomite, found in the limestone septaria at the Monroeville locality. Veins of barite up to 5 centimeters thick, sandwiched between ferroan dolomite, can be seen on the surface of most unbroken septaria. As these veins approach large pockets in the septaria the barite forms large bladed crystals. Isolated smaller crystals resting on ferroan dolomite also occur, but are less common. These smaller crystals are likely part of the same barite event, the only difference being the amount of the mineral emplaced.

The crystal form and habit are similar to the larger crystals, and the time of deposition appears simultaneous. Although it is common to find barite over 2nd generation ferroan dolomite, all of the barite seems to have been deposited between the 4th and 5th generations of ferroan dolomite. The reason for this is that pockets of 2nd generation ferroan dolomite are more common than pockets of 3rd or 4th generation ferroan dolomite. No examples of 4th generation ferroan dolomite on barite have been found. An excellent example of a complete isolated barite crystal on ferroan dolomite with calcite and aragonite is displayed in the photo to the left. This crystal is quite large in comparison to most isolated crystals which are generally less than 2 centimeters in size.

Barite Crystal Forms

Like celestine, a similar sulfate commonly found in Ohio, barite forms crystals in the normal class of the orthorhombic system. In fact, some local collectors have mistaken the barite at the Monroeville locality for celestine because of the physical similarities of the two minerals and the fact that celestine is more common in the nearby Devonian and Silurian limestones and dolomites. The barite crystals at this locality are generally tabular, although thin prismatic crystals as seen in the photo above have also been found. An illustration of this crystal form is labeled A in figure VI to the left.

This crystal form employs 4 macrodome (d) faces, 4 brachydome (o) faces and 4 unit prism (m) faces. The more common tabular crystals have 2 broad basal pinacoid (c) faces in addition to the faces found on the prismatic crystals, as illustrated by crystal B. However, the basic form is infrequently observed at the Monroeville site. More commonly, barite crystals will have an additional 2 macropinacoid (a) faces and/or 2 brachypinacoid (b) faces.

A crystal with both of these pinacoid faces is illustrated as crystal C. Rarely crystals will have multiple sets of 4 macrodome faces. These faces are generally thin and exist on either side of the macrodome (d) faces. Crystal D is an illustration of a crystal with a second set of macrodome faces. Crystals with up to 3 sets of macrodome faces have been observed at this locality.