MILLS GEOLOGICAL

Our featured specimen

Purpleheart ancestor (Peltogyne sp.)
Yegua Formation, Middle Eocene
Apple Springs Area, Trinity/Houston Counties, Texas
** A particularly handsome and also interesting specimen from a more tropical age of south Texas. The Yegua (pronounced “yeh-gwah”) Formation was the warmest and wettest age of the Eocene. Petrified woods of this era are typically preserved in strata that were deposited in near-shore habitats such as estuaries or deltas. As noted by Singleton in his 2017 paper on the Occurrence of Fossil Woods in Texas, the uplift of the Rocky Mountains along with substantial volcanism in the Four Corners region was producing abundant sedimentation that enveloped the trees during flood events as the material was being deposited in a subsiding Gulf of Mexico basin. The nature of the warm wet climate is shown in this specimen of broadleaf evergreen tropical wood by the rather indistinct growth rings which are more likely not growth rings at all, but rather are the result of occasional drought or low rainfall conditions, not annual growth. Modern trees in the genus Peltogyne (in the Legume subfamily of Caesalpinioideae) are now found only in tropical South America where conditions mimic those of the Texas Middle Eocene. So, there is plenty to love about this specimen for the story it tells and the beauty it displays – including a choice fortification agate structure in pale blue.
9" x 6.5" on the polished face; 5/8" thick slab $170

Willow (Salix sp.)
Yegua Formation; Eocene
Houston County, Texas
** Here’s a really handsome thick-cut slab with fantastic woody fine structure in addition to its aesthetic appeal. Despite its age of over 50 million years, it features the same very wide growth rings that our modern willow show. This slab was a mere youngster of 15 when it was already six inches in diameter! The growth rings are prominent and distinct. Houston County is not the home of the city of Houston. Old Sam Houston really got around and the county named for him is almost exactly midway between Houston and Dallas. The entire county is covered by outcrops of Eocene aged strata and this specimen comes out of the Yegua Formation. The Yegua Formation records a time of periodic sea level fluctuations and it was likely during one of the lower levels of the oceans that this log was trapped in the delta and covered with sediments carrying quantities of volcanic ash. It was this volcanic ash that provided the silica to petrify the wood. During other periods of the Yegua, the log would have floated out into the Gulf of Mexico, waterlogged and ended up on the continental shelf where it would have slowly rotted away. So, good luck for us petrified wood collectors that the Yegua had a low sea level periodicity! Be sure to look at the photomicrograph showing just a single annual growth ring with amazing preservation of structure!
6” x 5” on polished face; 3/4” thick slab $85

Elm surrounded by algae (Ulmus sp.)
Miocene, Trout Creek Formation
"Green Algae Wood Site" near McDermitt, Nevada/Oregon
** The so-called Green Algae Wood Site is just one of the many different diggings associated with the McDermitt area. But, it has long since been depleted and specimens now only come out of old collections - as did this one. The green color results from a trivalent form of iron oxide that colors the silicon dioxide as a trace element -- not because the living algae was green. Why this particular oxide colored only the algae and not the wood is somewhat of a mystery but it likely is the result of the algae being softer and more porous and for some reason the trivalent iron ions were only available at the very beginning of the petrification event. Later infusions of silica were much darker as a result of bivalent iron ions and perhaps an occasional trace of manganese as well as some of the bivalent iron minerals like biotite and olivine in the ash began to weather. If your collection does not have a representative specimen from this now depleted site, here is a chance to fill that gap. As you might imagine, with that much algae surrounding the wood, there was not a good prospect of the wood anatomy being well preserved. But, certainly enough remains to determine that this specimen is an elm.
4.5” x 3.5" on polished face; 7/16" thick slab $50

Tropical hardwood (Leptobalanus sp.)
Tertiary
Arajuno River, near Mishaulli, Ecuador
**A really interesting specimen with some remarkable provenance. The Arajuno River is a tributary to the Napo River and flows north and east from its source until joining the Napo River, just downstream from the village of Mishaulli. Just checking out the area on Google maps reveals that it is a tourist area of great beauty. But our specimen was not fished out of the Arajuno River by a tourist. Instead, it was a lucky missionary who found the deposit and he would bring back to California a load of specimens every few years on home leave. While on home leave, he would sell the specimens at local gem and mineral club shows. He had no idea what the taxon of the wood might be but we have identified it as a member of the genus Leptobalanus, a wood which has its own interesting history.

The wood, originally assigned to the genus Licaria,in 1981 was eventually reassigned in 2003 to the genus Leptobalanus (but both genera are in the same family of Chrysobalanaceae). A quick examination of the Insidewood website reveals that our wood is an exact match for Leptobalanus octandrus but we are constrained by international convention to not assign our fossil wood to the same modern species because the modern ones are described by reproductive structures (flowers, seeds, inflorescences, etc.) not wood anatomy. But look at the photomicrograph accompanying this offering. Initially, one might think that all of those parallel lines are growth rings but that would be incorrect. Those are all lines of parenchyma; this tropical hardwood does not have any visible growth rings because it grows at a constant rate throughout the entire year, and for year after year (one exception - extreme drought might cause a feature looking like a growth ring because growth is slowed down). Parenchyma cells store various food nutrients and water for times of stress when they can help prevent damage to the actual conducting tissue. Like all of the other cells in xylem, only the parenchyma cells next to the live cambial layer are functional. If they are not used, they simply continue storing the water and nutrients but cannot supply them to the cambial layer of growth. As you can see, the Leptobalanus genus really makes A LOT of parenchyma cells so this genus is always prepared for any stressful event. Now look at the vessels themselves and note how sparse they are. This is one of the lowest densities of vessels that you will see in any wood - tropical or otherwise. And, they are very small - considerably under 50 microns in size. So, it is a wood that operates at an odd set of extremes - minimal vessels but maximum parenchyma in case of trouble. The genus is native to the tropical areas of South America and particularly to the Amazon Basin - a small portion of which is in Ecuador. It is no surprise that the Rio Napo eventually empties into the Amazon River and flows to the Atlantic Ocean. If you like odd specimens with an interesting history, this one would make a great addition to your collection.
3" x 2.25" on polished face, end cut varies from 1 1/4" to 3/8" $55

Conifer (Pinales Order)
Silicic Ash Flow Tuffs, Middle Miocene
Duck Flat Valley, Nevada
** Here's an amazing survivor from a long-ago dig. There were at least three conifers fossilized in situ in Duck Flat Valley that showed just a little bit above ground and the remainder straight down below. This specimen came off of the side of a trunk that was 12 feet in diameter and 30 feet in vertical length. Almost all of the tree was excavated (as chunks) in the 1950s and turned into bookends and tumbled stone for the baroque jewelry popular at the time but now mainly resting in various landfills. So, the fact that this specimen has a center and that it was at the side of the trunk are indications that it was either a small branch or a root leading off of the trunk. It is just a stroke of luck that it was preserved at all but it was dug by the late Wally Marks of the Highway50/95 Rock Shop in Fallon, Nevada, and saved in a flat of wood that came out of that enormous hole. Today, the hole has a steel grating installed by BLM to keep people from falling in. The hole is perfectly round and exhibits some wood grain character on the sides when a light is shined down from above. All of that wood is now gone - imagine the tonnage that a 12-foot diameter, 30 foot long trunk would produce. I purchased this specimen in 2004 along with others from Wally's inventory after he passed away. Each specimen was labeled and wrapped individually in newspapers dated in the 1960s. This is a really unique opportunity to acquire a specimen with "bulletproof" provenance from a totally depleted site.
4.75" x 2.25" on polished face; end cut 2.75" thick $75

Opalized conifer (Pinales Family)
Volcanic sediments and flows, Miocene
Hackberry Wash, San Bernardino County, California
** A surprising find out of a very old collection. This locality is located within the Mojave National Preserve established in 1994 and rock collecting has been prohibited since then. But, as a practical matter, when I visited the site in the late 1980s, it was already totally depleted and I came away empty-handed so it is certain that the specimens we recently acquired from an old collection were collected in the mid-20th century. It is mostly white with black highlights and all of it is highly opalized making it very distinctive and unlike petrified wood from any other location. Simply put, there is very little from this location even in old collections I have learned, so if you are focused on different localities (like we are), this is an opportunity to grab this specimen.
2.5" x 2.25" on polished face; end cut up to 1/2" thick $48

Conifer (Pinales Family)
Trout Creek Formation; Miocene
Private Ranch near McDermitt, Oregon/Nevada border
** Here is a really interesting as well as beautifully patterned slab of coniferous wood from a new dig in 2015. One of our favorite diggers/cutters was authorized to use heavy equipment on a private ranch midway between the McDermitt Airport (Bretz Mine) site and the renowned Zimmermann Ranch diggings (both of which are west of McDermitt, Nevada along the Disaster Peak Road). This new dig, down almost 20 feet, uncovered some really great specimens and we were fortunate to get the best of the very best. Some of the patterning in this specimen is the result insect predation. If you have been collecting petrified wood for a while, you know that the typical insect predation is either tunneling perpendicular to the axis of the tree or tunneling parallel to the axis. These features are almost always created by different species of wood-boring insects. On the transverse face of the slab the result is either long sinuous trail (perpendicular to axis) or a perfectly round hole (parallel to axis). Check our two photomicrographs and note that this slab has both styles! And, there are a LOT OF TUNNELS, many with frass remaining. It is worth noting that the paper by H.D. MacGinitie entitled “The Trout Creek Flora of Southeastern Oregon” published in 1933 includes several genera in two different Coniferous families – Pinaceae and Cupressaceae among the fossil leaf flora collected in the Trout Creek Formation that has also produced this wood.
4.5” x 3” on the polished face; 3/4” thick slab $59

Fig (Ficus sp.)
Ricardo Formation, Pliocene
Last Chance Canyon, California
** Here is a small stand-up style fig specimen which is a rather scarce taxon in the fossil wood record of North America. It is from Last Chance Canyon, north of Mojave, California. The petrified forest at Last Chance Canyon in the El Paso Mountains was completely depleted by rockhounds and souvenir hunters long before the State of California established Red Rock Canyon State Park in this area and subsequently added Last Chance Canyon to the park. So, even if there were more petrified wood there now (there isn't), you would not be allowed to collect it! This piece was collected in the 1960s by a rockhound from Southern California. We think that the woody fine structure of this specimen is particularly good – see the accompanying photomicrograph and note the large size of the vessels (well over 100 microns), the abundant tyloses (crystals within each vessel), and the axial bands of parenchyma which links many of the vessels in lines. If you don’t have this taxon or this locality represented in your collection, this may be one of very few opportunities to fill that vacancy. As a standup specimen it is a bit unusual – both the top (dome polished) and bottom (flat-lap polished) have been finished.
2" x 1.5" on the two polished faces; stand-up varies in thickness from 1” to 3/8” $45

Ancient conifer (Pinales Order)
Columbia Plateau Basalts Group
Miocene
Southeastern Washington
** WOW! Maybe we could stop at that. Just wow. But … here is a spectacular larger slab with those growth rings about which we like to say, "...can be seen from across the room." There can be no doubt in the mind of any novice or non-collector that this is indeed petrified wood. It looks like it could have just come out of the local firewood yard, perhaps even dusted with snow for a yuletide fire. These beautiful larger slabs deserve a place on the wall or in the center of the top shelf of a display case. This was a relatively fast-growing conifer that enjoyed a good niche in the forest. Despite the size of the slab, we count less than 75 growth rings indicating that it had good sunlight, nutrients and water before being toppled and buried by a volcanic event and consequent ashfall. If you value superior aesthetics and "presence" this one has your name on it! This slab was never repaired (as most of you know, we are fanatics about disclosures of known repairs), but this slab is backed with fiberglass to help ensure its safety in transport.
13" x 8"” on polished face; 5/8" thick slab $295
(Immediately qualifies for our 10% discount on orders totaling $200 or more)

Unidentified wood (Incertae sedis)
Miocene
Santa Fe River, Florida
** Really nice small limb with amazing woody character. The Santa Fe River is a favorite spot for fossil seeking SCUBA divers to hunt for Miocene shark teeth and marine fish and mammal materials. Occasionally they also bring up small twigs and branches as well -- and that is the origin of this great limb. We have never cut one of these limbs to ascertain the taxon, feeling that the character of the limb itself would be compromised. It is likely that in addition to cutting and preparing a thin section off of this material, an acetate peel would be required to learn any more about its family, genus, and species affiliations. To be blunt - we like it just the way it is, no further investigation would make it better. Note the several knots of different size twigs that emanated from this limb. Outstanding specimen!
7/8" x 3/4" in cross section; 3" long $43

Conifer (Pinales Order)
Columbia Plateau Basalts Group, Miocene
Tygh Valley, Deschutes Canyon, Oregon
** Here's a locality that you will not see in very many collections. A good friend who is also a cutter and lapidary, grew up on a ranch in Tygh Valley, an area along the Deschutes River, about 40 miles upstream from the confluence of the Deschutes and Columbia Rivers. As it turns out, the ranch had some places where these neat conifer limbs could be dug and our cutter friend got his start digging petrified wood quite early in life! This was a very slow growing conifer - the growth rings are only about one millimeter apart making this one-inch limb around 25 years old when it was covered by a volcanic eruption and petrification began. Poor soil? Perhaps, since the conifers seem to do a lot better on poor (but well drained) soil than the hardwoods do. Could also have been too much shade, too little water or lack of nutrients. A tough life to end so explosively in a volcanic blast.
1" diameter on polished face; 3.5" long limb section $45

Ancient Redwood (Sequoia sp.)
Columbia Plateau Basalts Group Miocene
Saddle Mountain, Washington
** Exceptionally attractive and colorful specimen with very distinct center and with a branch leading off of the limb at the 9:00 position in our photo. In addition, the cutter topped it off with an exquisite polish. You will want to keep this one on display because every time you look at it, it seems you will see something different in the pattern. The rich variation in various reds and brown hues is the result of iron oxide (hematite) ions sneaking into the crystal lattice of the silicon dioxide (agate). It only takes a few parts per million to cause a color change and this specimen has many changes of color. Keeper.
4.5" x 3" on polished face; 5/8" thick slab $43

Limb cast (Incertae sedis)
Juntura Formation, Miocene
Stinking Water Creek, near Burns, Harney County, Oregon
** Stinking Water Creek is known for more than just petrified wood - it also has produced great common opal and beautiful plume agate. And, occasionally, just occasionally, we see a combination of wood with the agate/opal deposits. Here is a prime example of that interesting occurrence. The small limb sticking out of the agate is definitely a showpiece, especially if it is displayed alongside one of those fabulous Stinking Water opalized slabs and the two of them share space on the same label. Make it a triple and pick up a slice of fabulous Stinking Water plume agate the next time you see one and you'll have a real conversation starter. The Stinking Water area has a really interesting geologic history. The host rock is hyaloclastite with intermixed basalt pillows and capped by a basalt flow above the wood layer. Hyaloclastite forms when basalt lava flows into a body of water and rapidly cools, fragmenting into glassy bits. The openings between the pillows provide ample opportunities for weathering which then releases silica to provide the petrification of trees and the mass deposits of agate. The most likely explanation seen in the professional literature is that the basalt flow dammed a river, flooding the surrounding woodland. This shielded the trees, enabling their survival of volcanism without being incinerated. The capping basalt created an anaerobic environment for the wood, preventing decay by fungus, bacteria, or insects. The trees, now entombed in rock, were replaced slowly by silica from the surrounding rock. Additional silica, both opal and agate, was also deposited in conjunction with the petrification. The result? Instant collectible material for the serious collector. The Stinking Water locality was previously thought to be Pliocene in age, but recent dating by 40Argon/39Argon has determined it is actually older (Miocene) at 13.79 million years.
5” x 4” x 2" The limb itself is 1" in diameter $65

"Haw" or "Linden" tree (Viburnum sp.)
Mehama Volcanics Unit, Little Butte Formation, Oligocene
Sweet Home area, Oregon
** Well, it all depends upon where you are. Trees and shrubs of this genus in North America are called by the common name "Haw." while those in Europe are called "Linden." Call it what you want but this specimen is exceptional. Really fantastic preservation of woody fine structure. Check out the photomicrograph for this one. Note the vessels are almost entirely solitary - an occasional double but no long radial multiples. Rays are commonly 1 to 3 cells wide but can be even wider than that - all of them are present in this specimen. Growth rings distinct? Check! Vessels in the range of 50 microns, similarly sized throughout the entire growth ring? Check! How about density in the range of 40 to 100 per square millimeter? Check! Can you tell we think this is an exceptional specimen with great pattern and really wonderful woody fine structure? It even has a periphery of bark (real phloem). The Sweet Home petrified forest has produced a lot of fossil wood and we think that this specimen is at the top end of high-quality. It embodies everything that an advanced collector would want in a Sweet Home specimen. Please click photo for a more detailed view.
7.5” diameter on polished face; 1/2" thick slab $190

Pepper tree (Schinoxylon actinoporosum)
Laney Shale Member, Green River Formation, Eocene
Blue Forest, Wyoming
** This one has got lots going for it in addition to this great price! Excellent woody fine structure of the pepper tree along with a nice quartz crystal-filled cavity plus bits of bark floating in the baby blue agate around the 11:00 o'clock position. But wait -- there's more. Yes, easy to see borer tunnels - one of which is filled with frass (that formal botanical word meaning insect poop). Did we mention that there is a second heart where a small stem was forming right near the frass filled tunnel? There is simply a lot to love about this excellent specimen. If you are a Blue Forest enthusiast, it will surely be a good fit into your collection.
3.75” x 2.5" on polished face; 3/8” thick slab $45