gartrellite (w. calcite and duftite)

calcite; duftite; goethite (?)

Sub-spherical hollows (to 10 mm) in a matrix of calcite and goethite lined with crusts of well-crystallised dark-green duftite and minor black goethite, partly infilled by powdery, greenish-yellow gartrellite (EDS indicated; Frank Keutsch, Harvard University, 2025).

(This orbicular-like texture may have resulted from a botryoidal crust of duftite, possibly on goethite, over which a layer of calcite developed. The underlying matrix later dissolved away, leaving hollows under the duftite in which gartrellite precipitated.)

The specimen is from the A. P. Holden Collection, which was bequeathed to Harvard in 1913. This dates the specimen to the upper levels of the first oxidation zone (i.e. 6 Level or above).