Agate and jasper are actually chalcedony, which in turn is cryptocrystalline quartz. All are SIO2. When you pick up a stone you can rule out that it is a piece of regular massive quartz quite quickly just by looking to see if you can see the grains of the stone. If you can see grains, you do not have an agate or jasper. Most likely, what you have then is massive quartz or some other type of stone. Many new rockhounds will mistake massive quartz for a piece of agate, so don’t feel bad if you do. It’s a very frequent mistake.

Jasper and agate will appear to be made of wax. If the rock is just plain clear to white translucent with no markings or patterns, it is considered chalcedony. If it is opaque, that is, if you cannot see into or through it, it is jasper. Jasper is most frequently earth tones or red but you can find jasper in just about any color or color combination and it can contain some very lively patterns. One well known form of jasper is called “picture” jasper, and just as the name suggests, the lines and markings look just like a scenic picture of mountains and valleys or forests and so on. Geometric patterns are also common in jasper stones.

If a stone is an agate, it will be translucent as is chalcedony, but an agate will have patterns. Most commonly, agates have bands, and are appropriately called banded agate. Sometimes the bands are also translucent, sometimes some are opaque. There are many agates named to describe how they look, such as plume, orbicular, or flower and many that are named for the place they are found, such as Dryhead or Lake Superior. For instance, moss agate is a clear to semi-clear agate that looks like moss was embedded in the stone. No two agates are alike and many fantastically patterned stones will not have specific type or place names.

There are also stones which you will find that have both jasper and agate in them. Both the opaque and translucent parts of these stones will appear waxy. These are often referred to as jasp-agate. Once you become familiar with the look of both jasper and agate, you will be able to recognize jasp-agate with no problems. One other stone that can be confused with agate or jasper is opal.

Opal will have flashes of color if it is precious opal. It can be also be common opal which is plain translucent or opaque and a just about any color or a mix of colors. Opal generally looks more glassy than waxy, and it is much more brittle and breakable than agate or jasper.

If you still aren’t sure when you find a rock if it is jasper, agate, or opal, you should take it with you and ask someone about it. Your local rock shop or club or even a jeweler’s shop can identify it for you. You will have few problems identifying these stones after the first or second time. Once you learn to identify these basic stones, you will be surprised how many different types of gemstones you will start noticing on your hunts.

© Sally Taylor, RHS1

If you have a puzzling specimen sitting on the shelf that you just can’t identify or have other questions about mineral identification, you really don’t want to miss the 42nd annual open house at The Geology Museum at Rutgers, The State University of New Jersey, on January 30th.

At the open house people can have their own samples professionally examined.  There will also be a mineral sale for those looking to add some great material to their own collections, as well as hands-on geology activities for children.

Along with the rock and mineral identification program, earth science presentations include:
Earthquake Detection for the Citizen Seismologist 3:00 pm
Madagascar’s Buried Treasure: Dinosaur and other Vertabrate Fossils from the Land that Time Forgot 2:00 pm
Paleoclimatic Framework of Human Evolution: Examples from Olduvia Gorge 11:00 am
Monitoring our Ocean Planet: The Scarlet Knights Trans-Atlantic Challenge 10:00 am

Saturday, Jan. 30, 9 a.m. to 4 p.m.

The Geology Museum at Rutgers
The State University of New Jersey
Scott Hall
43 College Avenue
New Brunswick presentations in room 123
mineral sale in room 135
hands-on children’s activities in room 115.

Additional presentations in Geology Hall
85 Somerset Street
New Brunswick
rock and mineral identification, children’s activities in Geology Museum, 2nd floor