Microdenticles on naturally weathered hornblende

Microdenticles (with lengths in the micron-submicron range rather than tens of microns) are developed on the lateral surfaces of larger “classic” denticles on naturally weathered hornblende from weathered amphibolite of the Carroll Knob Complex in western North Carolina. Microdenticles share the shape and orientation of the larger more typical denticles, producing arrays of microdenticles that give the larger host denticle the appearance of a surface covered with imbricate pointed or rounded scales. The arrays of imbricate microdenticles are formed by low-temperature aqueous alteration during weathering of the Carroll Knob Complex hornblende; they are later-stage corrosion forms on already-corroded surfaces of hornblende that show larger-scale evidence of typical weathering. In the Carroll Knob occurrence, hornblende microdenticles are associated with dilute weathering solutions, suggesting possible control by extreme undersaturation of solutions with respect to hornblende.