Multiple Growth 2nd Generation Calcite


Perhaps the most interesting Calcite specimens are the multiple growth second generation crystals. This habit of Calcite is most easily recognized by the abundance of terminations on one or both ends of the crystal. However, the majority of Calcite crystals in this habit are only singly terminated. These crystals also have the distinction of being a deeper yellow brown color than the contrasting pale, clear first generation crystals. Regrettably, it is extremely difficult to collect a decent specimen of this particular habit of Calcite due to the size of the crystal in comparison to the size of the cavity.

Often, this habit of Calcite fills more than 3/4 of the fossil cavity. In addition, while this is a common growth form at many statewide localities, it is a highly uncommon habit at Georgetown. Add these conditions to the likelihood of breaking open the fossil cavity in the right direction so as to avoid breaking through the crystal and it becomes fairly evident why few of these specimens are preserved.

The photo to the Left displays a typical multiple growth crystal from Georgetown. Notice the size of the crystal in comparison to the overall size of the cavity. Calcite crystals of this habit, which have been saved, are generally similar in size to this one in comparison to the overall size of the fossil cavity.

Twinned Calcite

Although Calcite is known to form crystals in many habits throughout the state, twinned Calcite crystals are very rarely encountered at any Ohio locality. Surprisingly, small stretched out twinned scalenohedral Calcite crystals are occasionally observed in geodized brachiopods from Georgetown. These twinned crystals bare some similarity to 1st generation Calcite crystals from this same locality.

These twinned crystals are typically the same color and clarity of the average 1st generation Calcite. Also, although twinned crystals have been observed up to 1 centimeter in size, the average twin is approximately a quarter of a centimeter, similar to most 1st generation crystals. Because of these similarities, it is often difficult to tell 1st generation Calcite and 2nd generation apart at first glance. However, the two are easily separable with the aid of a hand lens. First, twinned crystals have a clearly visible twinning plane.

Twinned Calcite crystals, from Georgetown, are clearly scalenohedral in form, but are stretched out along the twinning plane creating a heart-like shape. This shape bares absolutely no resemblance to 1st Generation Calcite. The photo to the left displays one of these twinned Calcite crystals. Notice the clear twinning plane and the overall shape created by the stretched scalenohedron. The crystal above and slightly hidden behind the main crystal in the photo along with many other 2nd generation crystals in this pocket are also twinned in this same manner.

Twinned 2nd Generation Calcite

Other 2nd generation Calcite forms have been observed and more are possibly waiting to be discovered in geodized brachiopods of the Georgetown area. Additional forms which have been identified at this locality include Scalenohedral crystals with rhombic modifications and phantomed crystals. The first, modified Scalenohedral crystals, are easily identified by a “flattened” rhombohedral termination. Even a slight rhombohedral termination disguises the dominant Scalenohedral form can easily cause the collector to misidentify the crystal as a Sulfate. The crystal to the lower left exhibits this characteristic.

When viewed from an angle parallel to the the rhombohedral modification, this crystal greatly resembles Celestine. The color and clarity of this crystal contribute to this similarity. Rarely, brown phantoms have been observed in second generation Calcite crystals. Typically, these phantoms are found in scalenohedral crystals with slight rhombic modifications that are less than one centimeter in size.

Although the phantoms in these crystals are often clouded and indiscernible, phantoms contribute to the color and aesthetics of small, lusterless and somewhat unappealing crystals. The photo on top is a classic example of a phantom Calcite crystal from this locality.