Jasper or Agate: A Simple Distinction

Jasper and agate are the rocks we hobbyists deal with the most often in pursuit of our goals as lapidaries and collectors. Do we really understand the differences between the two?

Often confusion arises when attempting to describe a specimen as either jasper or agate. Both jasper and agate are composed of extremely fine interlocking quartz crystals called cryptocrystalline quartz. As such, they are both members of the fine-grained quartz family referred to as "chalcedony". Chalcedony occurs throughout the world in beds, bands, nodules, geodes, botryoidal masses, as a replacement of fossils, wood tissues or often other minerals, and as a cementing material. It is deposited from silica-rich waters, often carrying other mineral impurities. It is the presence of these mineral impurities which stain the micro-quartz grains to produce the wide variety of colored patterns, banding effects and inclusions that differentiate the basic "gem" forms of cryptocrystalline quartz-jasper and agate-from ordinary drab chalcedony.

So what is the difference?

In general, agate is a transparent to translucent form of chalcedony in which the coloration takes the form of regular bands, rings, clouds, wispy inclusions or distinct groups.

Agate containing straight or concentric bands is referred to as a fortification agate. Moss agate contains wispy or lacy inclusions of coloring materials, often the green mineral chlorite which penetrated cracks in the silica gel matrix prior to hardening. Now they remain as fine picture-like images. Agates are usually named by employing the geological area where it is found with a descriptive adjective, as : Priday Ranch Plume Agate".

Jasper, on the other hand, can be somewhat translucent but is most often opaque. The colouration of jasper is usually much darker than that of agate and is totally random with respect to distribution and pattern. Finely divided hematite gives the color to reddish jaspers, and another iron mineral - goethite- is responsible for yellows and browns. Chlorite and nickel minerals contribute to green conjuration. As with agate, jasper comes in many colors and displays almost an infinite variety of patterns. Because of these properties, it is an extremely versatile material for cabs, scenic "pictures" to be framed, and other functional and decorative purposes. It is truly the bread and butter "gem" of our hobby.