In this latest edition of the Type Localities series, we will be looking at Zaklodzie.
Zaklodzie is a Polish find that turned up on the side of a road in September 1998. It was found by Stanislaw Jachymek while he was out hunting fossils and rocks. The 19.1 Lb. (8.68 Kg) single stone find is a great example of the intriguing and contrary thought processes on how one might get to a similar meteorite composition by differing means, as reflected by the change in classification of Zaklodzie over time.
Early in 2000, the Natural History Museum catalog listed Zaklodzie as an Achondrite-ungrouped, while later the same year, the Meteoritical Bulletin updated its classification to Enstatite-rich-ungrouped. Six years later, MetBase listed the location as an Anomalous Aubrite. One more year after that on 26 June of 2007 the classification was yet again changed and set to Enstatite Achondrite-ungrouped, where it has remained for the past almost 20 years.
Zaklodzie displays some affinities to both the enstatite chondrites and the main named group of enstatite achondrites, the Aubrites. Differing proposed formative theories are evident in the tug-of-war displayed in the meteorite’s classification history. Proposed theories include it being a primitive achondrite formed on an enstatite chondritic parent body that a more global partially differentiated, a partial melt created on an enstatite chondrite parent body representing localized impact melting, or a cumulate magmatic formation from the Aubrite parent body, which is geochemically disparate from the other Aubrites. That all being said, it has enough differences from both groups to not be considered as a fit for either and is sitting with a select few other high enstatite achondrites of unknown parent body.
The count of Enstatite Achondrite-Ungrouped meteorites is very small and currently sits at 8 named localities. Of note, all are finds, and all 8 happen to be single stone finds. Though a few are in the double-digit kilo range, that means in total there is very little of this material around for study.
Zaklodzie appears to have a decent terrestrial age based on the extent of its weathering and formation of secondary minerals in the superficial regions of the meteorite, typical of an earthly high oxidation state. However, based on its decent mass, the interior material of the meteorite was much less terrestrially altered and provided a good glimpse at the highly reduced geochemical environment typical of all enstatite-rich meteorite classifications.
Metbul describes Zaklodzie as having a granoblastic texture consisting of approximately 60% enstatite, 20% metal,10% troilite and 10% feldspar with several accessory minerals to include schreibersite, silica, oldhamite, alabandite, and amphibole. Not mentioned in the write-up are the two minerals of interest to this article, which would be well into the “trace” quantity Browneite and Buseckite.
Browneite is named in honor of Patrick R. L. Browne, who was a professor at the Institute of Earth, Science, and Engineering, University of Auckland, New Zealand, who made major contributions to low temperature formation mineralogy and petrology. It is quite fitting this particular sphalerite group mineral is named in honor of Browne, seeing as it is the low-temperature dimorph of the above-mentioned alabandite found in trace quantities in Zaklodzie. Browneite forms at temperatures below 200 degrees Celsius. The mineral was first published in 2012 in the 97th volume of American Mineralogist, and its approval status as a recognized mineral was granted the same year.
Buseckite is named after Peter Buseck of Arizona State University to honor his work in the field of geochemistry and mineralogy related to meteorites and his associated work on high-resolution transmission electron (TEM) microscopy. The new mineral is a member of the Wurtzite group with a chemical formula of (Fe,Zn,Mn)S. It was approved by the IMA in 2011. Wurtzite, for which the grouping is named has the formula (Zn, Fe)S, so Buseckite is an iron analog to Wurtzitie as well as Rambergite (MnS) and is considered a polymorph of Browneite.
The finder with single stone find in hand. Photo credit: Andrzej Pilski
A thin section made by the author viewed with transmitted cross-polarized light at 44X.
