The 2111 pyribole chain sequence, where 2 signifies a double (amphibole-like) chain and 1 indicates a single (pyroxene-like) chain, has been reported from geological samples. Such material is commonly associated with slabs that contain multiples of three single chains, which we shall call "3n single-chain slabs" (where n = 1, 2, 3,... ). We generated 2111 chain sequences and associated 3n single-chain slabs by heating natural chesterite crystals at ca. 1000 °C in the laboratory as well as by their prolonged irradiation inside a 200 kV transmission electron microscope. Many of the synthesized 2111 sequences are intergrown with narrow regions containing isolated single- and double-chain material that contains, respectively, 3n single chains and n double chains. The single-chain triplets presumably formed as a result of the decomposition of isolated triple-chain slabs that were originally intergrown with the chesterite. The 2111 sequence and the 3n single-chain slabs can form, respectively, by decomposition of chesterite and triple-chain material during observation or perhaps during ion milling. Recognizing such artifacts is important when attempting to interpret geological history from the details of biopyribole structures and intergrowths.
ASJC Scopus subject areas
- Geochemistry and Petrology