Geodes 101

It is important to remember when talking about Geodes that not all geodes are the same. In fact most geodes from different areas are extremely unique to the area in which they are found. Another interesting fact about Geodes is that the naming of geodes is generally left up to whoever discovers them. Which means in some cases the names of certain types of geodes can become skewed when transferring from the miner, to the dealer, to the end consumer. Many times the dealer will put a more appealing name on the geodes in order to make them sell better. So when searching for information on geodes it may be more effective to search for the area in which the geodes come from in order to obtain more accurate information. Another very common mistake people make is assuming that every round rock they find is a geode. Even if the round rock has a Chalcedony (Agate) center it still does not make the rock a geode. In fact there is a very wide variety of igneous and sedimentary rocks that may look like geodes from the outside but may instead be Nodules, Concretions, Geodes, or maybe even just Rocks! Below I have listed some common terms that will help you become more educated in

Rock Hounding Terms

Geode: The word Geode comes from the Greek word Geoides which means “earthlike.” A
scientific explanation for a geode would be: a natural inorganic object, most often Chalcedony, which is hollow on the inside. Geodes are most often somewhat spherical and can occur in igneous or sedimentary rock. The interior may be lined with crystals, including quartz as well as other minerals pointing towards the center.

Nodule: Aggregate consisting of a spherical lump, usually from groups of small crystals. In other words it is what a geode becomes when it gets completely filled in, leaving no hollow pocket inside.

Concretion: A hard, compact, rounded, normally sub-spherical mass or aggregate of mineral matter formed by solution often around a nucleus. Concretions normally form in the pores of sedimentary or fragmental volcanic rock and are usually of a composition widely different from that of the rock in which it is found, and from which it is rather sharply separated.

Sedimentary Rock: Rock formed by the weathering of substances; forming layers from accumulation of minerals and organic substances.

Igneous Rock: A rock or mineral that solidified from molten or partly molten material, i.e., from a magma. Lavas and basalts are igneous rocks.

Metamorphic Rock: Pertaining to the change in the mineralogical, structural, or textural composition of rocks under pressure, heat, chemical action, e.g., which turns limestone into marble, granite into gneiss, etc.

Enhydro: Geodes which contain water.

Chalcedony: (pronounced kal-sid- knee) A cryptocrystalline variety of quartz. It is commonly microscopically fibrous, may be translucent or semi-transparent, and has a nearly wax-like luster. Chalcedony is a catch all term that includes many well-known varieties of cryptocrystalline quartz gemstones. Chalcedony is found in all 50 States, in many colors and color combinations, and in sedimentary, igneous, and metamorphic rocks. Chalcedony includes agate, sard, plasma, prase, bloodstone, chrysoprase, flint, chert, jasper, petrified wood, and petrified dinosaur bone just to name a few of the better known varieties.