Sentence:  The customary transitions of pitchstone are, into Chalcedony, Chert, Semi-opal; also into a substance resembling <WSD>conchoidal</WSD> shining jasper, found in clay strata, entangled in trap, or volcanic rock; and lastly, into Trap. 
Meaning of the word marked with <WSD> tags:  That fractures with planar concentric curves (e.g., as flint, chert or obsidian).