The Geolapidary Museum’s Baker Egg Mine Thunderegg Basics

The Baker Egg Mine (formerly known as Baker Ranch Agate Mine) is located 35 miles southwest of Deming, New Mexico, this nodule deposit is unique in the fact that these nodules are thundereggs (geologists know them as lithophysae) and carry all the rich colors, and more so, usually found in other species of nodules known as amygdaloids such as the famous Laguna agates of Mexico, the Condor agates from Argentina, the Agate Creek amygdaloids in Queensland, Australia and other world-class agate deposits. Most thundereggs are gray-blue or blue and white. Some thunderegg deposits produce hues of red or yellow from iron and sometimes black from manganese, however, most hold to a habit of one or two colors.

Andesite and basalt lavas contain more of the heavier minerals necessary to deposit the colors in amygdaloidal agates in which they are found. While most amygdaloidal deposits also produce dull, blue or gray nodules, there happens to be many deposits of amygdaloids in the world with multicolored agates while the Baker Egg mine is the only known thunderegg deposit in the world with multicolored agate.

Lithophysae (thundereggs) are found only in rhyolitic lava flows and domes. The rhyolite is molten granite that has separated into two components before or upon erupting to the surface. One is the crystalline remainder of the other which has been completely melted and reduced to a glass called perlite. The thundereggs are found in the perlite, most often more numerous near the contact with the crystalline rhyolite where many may be stuck to it. In most deposits, the perlite is reduced to a clay called kaolinite and the “eggs” are easily removed. In others, especially on steep slopes where erosion removes the clay as fast as the perlite decomposes, they must be dug out of the grayish to black glassy unaltered perlite. Rhyolitic lava does not contain the heavier metals found in andesite and basalt from which the colors seen in amygdaloidal agates have been transported and deposited, except for iron, which produces hues of red through yellow in some thunderegg deposits. But multicolored agate in thundereggs is very rare except for those found at the Baker Egg mine.

In my CD-ROM, “The Formation of Thundereggs” I advanced a hypothesis to account for how the thundereggs at the Baker Egg Mine are so richly colored. The area in which this rhyolite-perlite lava is in, is surrounded by “swarms” of andesite and basalt dikes and flows. The ground over which the rhyolite flowed some 30 million years ago, was thrown into episodes of breaking and thrusting, leaving fissures which were filled with andesite and basalt magma. Hence, over millions of years of erosion and leaching of the coloring minerals from the dikes by percolating (advection) ground water, the coloring minerals were transported through the perlite and colored any agate-filled thunderegg they came into contact with.

Crystal stalactites are at best found as anomalies in a few other deposits of all species of nodules and in fissure fills (vein agate) that have not filled solid. The Baker Egg Mine is the only deposit where this phenomenon is seen in an astounding 10% of every nodule we cut. Centered in most of the crystal stalactites you will see a feathery, whitish plume around which the quartz crystals grew. In the bottom of the cavity, many have a similarly colored level “floor” which is composed of the same material the plumes are.

We know the correct orientation because we know how these stalactites form. It is obvious that the floor is at bottom. These stalactites, unlike those that grow in the air of limestone caverns by evaporation, form in water-filled cavities from clay particles so small, they form a colloidal dispersion. Some attach to the top of the cavities and grow filaments downwards while the excess and larger particles settle to the bottom to form the floors. This same phenomenon is seen today as the iron rust particles that form the stalactites hanging from the Titanic in the deep, still waters of the Atlantic.

Some of the Baker Egg Mine thundereggs are hollow and lined with clear sparkling quartz crystals. When any species of a nodule is hollow, it is called a geode. There has been much confusion among rock hounds that thunderegg is a term for a solid nodule while, if it is solid, it is called a thunderegg. If one looks up geode in Webster’s Collegiate Dictionary, they will find that geode just means a hollow rock, “often lined with crystals” Thunderegg is a name given by the Warm Springs Indians of North-central Oregon to the nodules found scattered in places where they lived. Broken open by weathering, the white and translucent blue-gray halves look like a broken egg. The Indians believed, as legend has it, that these “eggs” were over cast missiles from the gods during periodic violent volcanic eruptions of Mt. Hood and Mt. Jefferson, just like the one I saw at Mt. St. Helens on May 18, 1980. Even to this day, tourists can hunt, fish, swim, etc., but anyone is forbidden to pick up thundereggs. In fact, I knew two ladies, a mother and daughter, who were forced to walk five miles to the jail on the Reservation for collecting rocks and dead wood for their garden, and that was in 1960.

Any thundereggs you buy from me, are guaranteed to your satisfaction or your money will be refunded.

If you check the market for comparable prices on agates such as Laguna, Condor, Agate Creek, Nova Scotia and others, you will find our prices are at wholesale and are unmatched in quality. To keep our prices low, we do not take credit cards. To order, please either call or email us.