As with many of the vague terms used to describe the various microcrystalline quartz forms, the exact definition of “jasper” has never been officially determined.

However, with a name derived from the Old French for “spotted or speckled stone”, most jaspers include more than one color and the various sub-variety names often describe what the resulting color patterns most closely resemble (e.g. leopard skin jasper, orbicular jasper, ribbon jasper, zebra jasper, poppy jasper, etc.).

While the above could also be equally applicable to agates, it is the stone’s translucency, or a lack thereof, that differentiates these two chalcedony groups, with most varieties of jasper being completely opaque. This distinction can be most clearly seen when comparing the visual appearances of opaque moss jasper and the similarly-named, translucent moss agate.