Jasper closes the list of twelve breastplate stones in Exodus 28, assigned there to the tribe of Benjamin, the youngest of Jacob's sons, a placement medieval and modern commentators alike have sometimes read as fitting for the final position in the sequence. Jasper's wide natural color range, red, yellow, brown and green varieties all occur, made identifying "the" biblical jasper with a single modern variety a matter of some scholarly disagreement, since ancient naming conventions for stones did not map neatly onto the more precise mineralogical categories used today.
Modern gemology treats jasper as an opaque, fine-grained member of the chalcedony family, distinguished from clearer chalcedony varieties like carnelian and agate primarily by its density of mineral inclusions, which is what makes it opaque rather than translucent.
The name itself is one of the few in the list that can be traced with some confidence. The Hebrew yashepheh, the Greek iaspis of the Septuagint and the English jasper are the same word carried across three languages by borrowing rather than three independent coinages, which is unusual in a list where most of the names travelled less cleanly. What the word denoted is a separate question from where it came from, and several ancient uses of iaspis appear to describe a green translucent stone rather than the opaque material a modern catalogue files under the name.
The Exodus list is also not the only stone list in the Hebrew Bible. Ezekiel 28 names a set of precious stones that overlaps it, and the Hebrew and Greek texts of that passage do not carry the same number of stones as each other, which complicates any attempt to read one list against another as a check.