Sulfidic travertine from the upper Cenozoic of Indonesia.
This attractive material is called "Bumblebee Jasper" or "Mustard Jasper", in reference to its color. "Jasper" is a rockhound/lapidarist term for finely crystalline quartz, but Bumblebee Jasper is not quartz - it bubbles in acid. Chemical analysis has confirmed that it is calcium carbonate (CaCO3 - calcite). The coloration is from various microscopic mineral inclusions. The light to medium gray areas are ~inclusion-free calcite. The dark gray to black bands are from pyrite inclusions (FeS2 - iron sulfide, also known as "fool's gold"). The yellowish and orangish areas are from realgar inclusions. Realgar is a reddish-colored arsenic sulfide mineral (AsS). In the form of very small, disseminated inclusions, it has a yellowish-orangish color.
Bumblebee Jasper has a finely-, but irregularly-banded structure. The calcite itself is fibrous. Banded, fibrous calcareous rocks are known as travertine, which is a chemical sedimentary rock. Travertine is commonly encountered in caves, in the form of speleothem - stalactites, stalagmites, columns, flowstone, etc. Travertine also forms at many hot springs. Bumblebee Jasper appears to be travertine deposited in a volcanic solfatara area, with signficant iron, arsenic, and sulfur impurities.
The deposit is reported to be near the base of Mount Papandayan, a subduction zone stratovolcano in Indonesia. However, I have seen no site descriptions, locality photos, or detailed maps. I have been told that the Mt. Papandayan locality information is inaccurate, and that Bumblebee Jasper is found at three sites in western Java: near the town of Ciniru (Kuningan Regency), near the town of Cirebon, and in the Bandung area.
Locality: unrecorded/undisclosed in Indonesia (but attributed to near Mount Papandayan, western Java)
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See info. at:
Fritsch & Ivey (2015) - Mustard Jasper or Bumble bee stone. 34th International Gemmological Conference, August 2015, Vilnius, Lithuania: 149-150. (pdf - see pages 149 to 150 of this file:
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