The original unedited submission to Rock & Gem Magazine, 2020

NEW GEOLOGIC MYSTERIES FROM THE CARVER AGATE FIELD

By John L. Carver and Bill Halepeska

The Alpine, Texas, ‘Carver Agate Field’ has presented a new and still unsolved geologic mystery. Last year a large caliche pit being excavated on The Carver unexpectedly exposed a very small ‘pocket’ (approximately 30′ x 50′) containing over a thousand agate nodules many of which were geodes (nodules with a hollow inside). The bottom of the ‘deep pocket’ is 15’+- below from the present ground surface, with caliche located nearer to the surface. There is an ashy greenish\white material surrounding the nodules. Significantly, around the nodules and geodes there is no sorting of material by size or layering typical of water deposited materials! Many of the geodes contained gorgeous amethyst, smoky quartz, and citrine crystal filled cavities. Other geodes contained beautiful calcite crystalline specimens mixed in with the smoky quartz crystalline geode interiors. Some of the nodules are stunning deep blue banded agate, some have extremely fine blue banding and very petite sparkling crystal centers. Interestingly, the ‘deep pit’ nodules lack the color and sagenitic variability which has been the hallmark of agates from The Carver agate field.

The Carver has typically produced multi-colored nodules, geodes, and agates, e.g., green, pink, red, yellow, blue, purple, and orange; whereas, the ‘deep pit’ nodules and geodes and agates are primarily either blue, gray, or colorless agate many with smoky quartz, amethyst, or citrine hollow centers. While the blue agates’ amethyst, smoky and citrine crystal filled geodes are spectacular in their own right, the lack of diverse coloration and varied inclusions which have characterized The Carver raises some important and interesting questions. These more typical color variable inclusion laden agates and geodes can been seen in extensive picture galleries at my website, TexasAmethystAgate.com, and were the subject of prior articles published in Rock & Gem, Vol. 47, issue 8, August 2017, page 10, Does the Material Match the Hype?; and Rock & Gem, Vol. 48, August 2018, issue 8, page 16, The Unicorn Citrine Scepter and Yellow Agates.

Only two types of agates are found in the ‘deep pit’, e.g., banded and fortification agates. Except for the ‘deep pit, The Carver has historically produced the following agates (in many varied colors): plume agates, fortification agates, fragmented filament agates, brecciated agates and jaspers, eye agates (orbicular), dendritic agates, picture agates, scenic agates, sagenitic agates, jasp-agates, layer agates, moss agates, and tubular agates. Before agate purists get too excited, I know some of what I have listed are not considered by purists to be true agate types. The list I have made is demonstrative of the diverse type of material historically found on The Carver except for the ‘deep pit’. This degree of diversity is exceptional even for West Texas agate fields. Most agate fields display a limited range of coloration and\or agate types….such as I have found within the ‘deep pit’ material! Many other agate fields have somewhat limited types of inclusions, coloration or types of agate that allow some experienced rock collectors to examine a specimen and to identify the general area where found and often the exact name of the agate field where collected. Examples would be Deming, NM, nodules; Balmorhea blue agate (from Balmorhea, TX); Woodward ranch plume agate; Walker ranch moss agate; Laguna agate from Mexico; Great Lake agate….the list could go on and on. The point is that material from each of the listed agate fields have characteristics which, while perhaps not unique, are common to a particular agate field. The immense diversity of material previously found on The Carver is, I believe, remarkable. So, it is odd to find among such diversity on The Carver, a small pocket with hundreds or thousands of geodes and nodules with a limited coloration, and sagenitic diversity from what has been found on The Carver over the last 12 years! While it is true that smoky and amethyst quartz geodes have been found for years on The Carver, those previously found geodes have major interior and exterior appearance differences (from the ‘deep pit’ material) which clearly suggests to me a different formative location and\or process.

There are other significant differences between The Carver and the recently discovered ‘deep pit’ material. There is a total lack of jaspers, jasp-agates, or brecciated material in the ‘deep pit’. The Carver is notable for its wide spread formations of red, yellow, green jaspers, jasp-agates, and brecciated jasp-agates. However, no jasper of any type or color has been found with the ‘deep pit’ material! There is one other major difference between the ‘deep pit’ nodules and geodes and most of the nodules and geodes found on the rest of The Carver over the last 12 years. The ‘deep pit’ nodules are almost never deeply fractured or ‘cracked’, while nodules found on the rest of The Carver are very often heavily cracked or fractured, and often broken. This suggests to me that the ‘deep pit’ material either formed differently from the rest of The Carver agate field, or that the ‘deep pit’ material formed elsewhere away from The Carver and was somehow carried to the ‘deep pit’ on The Carver by a means that did not pick up and deposit in the ‘deep pit’ the varied jaspers and agates so common all over the rest of The Carver agate field.

While the uniformity of the ‘deep pit’ material compared with earlier Carver field finds is of geological interest to me, of equal geological interest is the extremely small area containing the ‘deep pit’ nodules and geodes with virtually none found elsewhere in a fairly large excavated pit area (approximately 700′ by 900′)! The ‘deep pit’ nodule\geode sizes ranged from 15+ pounds to smaller than a fingernail. Some of the geodes have rinds that are so thin, 1/8″ of less, that they are subject to breakage while being clamped into a diamond saw for cutting! This fragility of some thin geode rinds of some of the ‘deep pit’ material is an important clue to solving the ultimate geologic mystery of whether the ‘deep pit’ material formed where found or were formed elsewhere and somehow transported to their current location in the ‘deep pit’!

This raises the question of whether the ‘deep pit’ nodules formed in pockets formed by gas bubbles in the lava (while still molten) at this small 30′ x 50′ area and then weathered out; OR, did they form in lava elsewhere and erode out, only to be somehow carried to this location? The other possibility is that these nodules\geodes formed in the location where found (approximately 30′ x 50′) and for some reason did not form anywhere else in the much larger 700′ x 900′ area of the ‘deep pit’? Were they somehow formed in this one tiny discreet location but not formed in gas bubbles in lava? Two different geologists with extensive experience in West Texas have examined the ‘deep pit’ site and suggest two totally different formative possibilities. One geologist suggests that the ‘deep pit’ geodes and nodules formed elsewhere in gas bubbles in lava, eroded out of the lava, were carried to the ‘deep pit’ location, and later buried by overburden. Another geologist suggests the nodules may have been formed in the ‘deep pit’ location where found but not were formed in gas bubbles in lava! Which theory best fits the ‘deep pit’ nodules and geodes?

An additional possible clue in the mystery is that the ‘deep pit’ geodes\nodules’ exteriors are almost uniformly un-fractured or undamaged! They lack the type of surface damage which would be expected had these geodes\nodules weathered out of a lava gas bubble matrix and then been carried by water to this ‘pocket’. Other than damage by heavy equipment excavation, the ‘deep pit’ geodes\nodules are mostly unbroken and\or chipped as would be expected if they had been bounced against each other in a water flowage or stream bed with a water flow capable of transporting some nodules weighing up to 17 pounds! (It is noteworthy that many very large and small nodules and geodes were found mixed together in this small pocket.) Also, if these geodes\nodules were part of or transported in a stream bed, there would likely be other rounded\smoothed and\or chipped ‘non-nodules’ in the pocket! There are very few, if any, rounded and smooth non-nodule material found surrounding the geodes and nodules in this small pocket. The nodules were found in an unsorted hodgepodge surrounded by a fine white/green material believed to be tuff (hardened or semi-hardened volcanic ash). While the ‘deep pit’ overburden contains water shaped rounded non-nodules, the small ‘deep pit’ does not. Were the nodules and geodes formed in gas bubbles in lava here or in the white ashy material where found? The geodes\nodules’ exterior surfaces appear to reflect the rounded shape of the gas bubbles in the parent rock in which they were originally formed. I believe the ‘deep pit’ nodules were formed in gas bubbles formed in molten lava. The majority of the nodules and geodes from this pocket have a classic roundish top with a flattened bottom shape reflecting formation in lava gas bubbles which have a flattish bottom, and round ‘top’. Conversely, nodules and geodes that form in volcanic ash (Deming, NM, nodules for instance) and other non-volcanic materials (see 2019 Rock & Gem article about this) instead of in lava gas bubbles, have interiors and exterior shapes that are more often not flat bottomed and/or almond shaped. Hence, even though the ‘deep pit’ nodules are found surrounded by a fine ashy looking material, I don’t believe they formed in or from that ashy material because of the flat bottom, rounded top, and/or almond (amygdaloidal) shape. I also note that the ‘deep pit’ agates have classic agate banding which is usually different from geodes and nodules not formed in a lava gas bubble.

So, I conclude that ‘deep pit’ nodules\geodes formed in and then weathered out of gas bubbles which had formed in lava before hardening. Since these nodules and geodes are only in one small area in the ‘deep pit’, I don’t believe they were formed and\or weathered out in the location where now found. I believe they were formed elsewhere and carried to the ‘deep pit’ location by some means. I have ruled out water transport due to the highly variable nodule size which if transported by water would have broken and\or shattered the thin rind ‘egg shell’ geodes found in the ‘deep pit’. Likewise, the noticeable lack of surface damage, and lack of water sorting by size or layering of the material in which nodules were found argues against water transport. The single limited location where found in the ‘deep pit’ (which does not appear to have layering or sorting as expected in a stream bed) also argues against water deposition. I exclude glacial transport because there is no recent documented glaciation so far south in Texas in the last approximately 25 million years after volcanism ended in this area. So the ultimate mystery is: if the ‘deep pit’ nodules were not formed in the ‘deep pit’, and they were not carried there by water, how did they get there and where did they come from?

My friend, geologist Bill Halepeska, of Midland, TX, believes the nodules formed elsewhere in gas bubbles in lava, weathered out, and were then carried to and deposited in the ‘deep pit’ by a volcanic mudflow. This theory explains the generally unblemished, undamaged nodule exteriors, and the fact that very thin rind geodes survived transport (along with 17 pound monster nodules) without being crushed or broken. This mudflow would have been slower than water and would have cushioned the impact between nodules carried by the mud! This also explains the fine ashy volcanic nature of the materials in which the nodules are now found. The mudflow theory also explains the lack of layering and\or gradation of materials by size as would likely be seen in stream bedding either around the nodules where found or elsewhere in the 700′ x 900′ pit. The mudflow theory seems to best explain this tiny nodule pocket, EXCEPT for the final mystery.

It also appears likely that the ‘deep pit’ nodules and geodes originally formed from a volcano different from or away from the volcano which created the amazing diversity of color and sagenitic material and jaspers found on the rest of The Carver agate field. This would help explain why the ‘deep pit’ materials contained no jasper and or diverse agate coloration. The geology of the area suggests the ‘deep pit’ geodes, nodules and agates formed from another volcano west of The Carver and were transported to The Carver by an ancient volcanic mudflow!

How did a volcanic mudflow pick up a large quantity of nodules and geodes and deposit them together in such a small 30′ x 50′ area but not in the rest of the larger caliche pit? While further future excavation of an even larger pit area may definitively answer the question , for now the best explanation is transport by mudflow.

New Discovery: Geologist Bill Halepeska’s view point

A deposit so obviously different from finds elsewhere in the immediate area has been discovered by rockhound John Carver on The Carver agate field near Alpine, Texas. John found significant quantities of the agate nodules, and amethyst and smoky quartz geodes among the road materials being used to maintain area roads. A search for the source led him to the pit from which the road material had been removed. Additionally, he found that the materials of interest (agate nodules and geodes) seemed to be coming from a very limited area within the large pit. He named this small pit within the larger pit the ‘deep pit’.

The “deep pit” site is located within The Carver agate field near Alpine Texas and near the Paisano volcano which is located west of Alpine. I personally visited the site and observed several interesting conditions. Apparently, the pit area was sufficiently lower than surrounding areas, and was the frequent repository of incoming debris. Study of the north wall of the pit clearly indicated multiple flows. These materials consisted of fine grained ash/mud debris containing little or no larger objects. Some of these finer materials seemed to consist mostly of carbonates from eroding limestone. One ash/mud flow carried very large pieces of rhyolite. Of particular interest was the near total absence of any nodules or geodes within the larger pit area from which the ‘deep pit’ area yielded large quantities of materials of interest. Further observation over the entire large pit yielded none of these materials. Except for the near surface deposits and topsoil, horizontal layering is absent. As for the lower deposits, clear contact planes were at varying angles.

Obviously little, if any, of the observed fill (debris) seen here came from areas to the east where agates and jaspers in widely varying colors are found in abundance. Where, then, is the probable source of the ‘deep pit’ material (nodules and geodes)? A review of the general area to the west did reveal some likely prospects. The Paisano volcano (peak and caldera) is located about 12 miles west-southwest of Alpine and is cut by Hwy. 90. This volcano produced a shield-like area of lava with a volume of approximately 150 km3. For non-geologists, this is a gigantic volume. Flows trending to the north and east consist of about 60% quartz trachyte, 25% trachyte and 15% rhyolite. Materials also consist of small ash flows and agglomeritic tuffs. The south-east portion of this shield is shown to extend eastward in an area south of Alpine and east of HWY. 118. Also, Alpine Hill located .5 mi south of Alpine and west of Hwy. 118 is a quartz-syenite intrusive. (1) It is my belief that the geodes and agate nodules recovered from the ‘deep pit’ originated in this area and transported to the pit as post-volcanic debris flows. The “deep pit” material of interest seems to be coming from a small area in the west end of the larger pit identified by a small entrance profile some 15 x 20 feet in size. The transported flow material entered the area, moving through a “channel” not unlike the dry washes seen around the area. Additionally, I believe that this debris profile once extended eastward through the larger overall excavation. The numerous elongated, teardrop shaped agate nodules and amethyst and smoky quartz geodes would ordinarily be found within a lava matrix exhibiting expanding gas vesicles and not in ash/mud material. Geodes, on the other hand are often found in similar environments. While the very fragile objects observed in the ‘deep pit’ could have been developed here in situ, I believe that the nodular agate and geode material was formed elsewhere and transported to this location carried in a thick ash\mud medium moving in minimum to non-turbulent flow, hence the absence of many geode\nodule fragments. The ‘deep pit’ agate nodules and geodes apparently came from the Paisano volcano and not from that which formed the highly diverse and colorful Carver agate field materials.

(1) Bureau of Economic Geology, Guidebook 23, “Igneous Geology of Trans-Pecos Texas” 1986 and Guidebook 19, “Cenozoic Geology of Trans-Pecos Volcanic Fields of Texas”, 1979

In the meantime, I would invite others to let me know of their thoughts about the mystery and other possible geological explanations. Since we already have two very knowledgeable and experienced geologists with two different theories, feel free to join the discussion. You can explore a great many more photos of the mystery ‘deep pit’ geodes and nodules at my website, TexasAmethystAgate.com. I would invite you to my website to make your own comparison of the vastly different look, color, and nature of the ‘deep pit’ material versus the diverse material previously found on The Carver.

EPILOGUE

No, I did not go hunting for amethyst geodes in a caliche pit!
Although not the real purpose of this article, some may be interested in how this ‘deep pit’ discovery occurred. Certainly the geological difference between caliche and amethyst geodes and blue banded agates would not suggest that rock hunting in caliche pits is productive actively. In fact, the ‘deep pit’ discovery has a more serendipitous story. In the fall of 2018 I was hunting for ‘cool’ rocks in water diversion ditches recently cut by a grader to carry water away from ranch roads. Where a water diversion ditch encountered the edge of the ranch road, I spotted a grapefruit size, flat bottom, rounded top rock that had the shape of an amygdaloidal (almond shape) nodule formed in a lava gas bubble. The shape alone told me what I had found. Extensive previous rock hunting in the immediate area told me that my fortuitous find did not make sense. First, the nodule was of gigantic size compared to what I had previously found in the same area. Second, the exterior of the nodule was much smoother and ‘un-weathered’ from what I had usually seen in the area. Third, the nodule had a greenish\white color from a powdery material which lightly covered its surface. I almost immediately concluded that it came from somewhere else. Since there had been some recent road repair, I suspected it may have arrived with the caliche. I had been to lots of old caliche pits on this ranch and concluded a long time ago that you do not find anything much in caliche. Curiosity aroused, however, I went looking for the source of the caliche and found the ‘deep pit’. I searched the whole pit area and found nothing except in one area about as wide as a large dozer blade and maybe 30 feet long. This was clearly the source of all the ‘deep pit’ material seen in this article and pictured in ‘deep pit’ galleries on my website, TexasAmethystAgate.com. I think there may be a lesson here, but I am a rocker not a philosopher! Good rocks are always where you find them!

GEOLOGIC MYSTERY ARTICLE – PHOTOGRAPHS AND CAPTIONS

All photos are by John L. Carver

Photo 3137: This cross-section of blue banded agate geode with flattened bottom and rounded top is indicative of its formation in a lava gas bubble.

Photo 3189: This very large blue banded agate nodule with flattened bottom and rounded top does not resemble Deming, NM, nodules which form in ash not in lava gas bubbles.

Photo 3192: This is a large amethyst geode with small blue banded agate nodule attached. NOTE: flat bottom and rounded top are indicative of formation in 2 lava gas bubbles.

Photo 3249: This shows a classic flat bottom, blue banded agate geode with euhedral smoky quartz crystal center with white secondary crystalization and brown colored calcite crystals intruding into geode center. Ash formed nodules and geodes do not usually have this type of banding.

Photo 3264: This is an amethyst druzy from a geode’s hollow center. Amethyst is quite rare in Texas but is fairly prevalent on The Carver.

Photo 3280: This is a fragile thin rind geode with a calcite crystaline center which likely would have been broken had it been transported by water to the ‘deep pit’ along with other large stones.

Photo 3281: This is a classic amygdaloidal (almond shaped) blue banded agate smoky quartz geode with prominent yellow sagenitic (star burst). NOTE: very soft, yellow\green ashy material on exterior (top and right) in which the geode was bedded.

Photo 3302: This a bluebanded agate nodule with euhedral quartz center. This kind of banding is not like the banding seen in agates formed in ash deposits.

Photo 3108: This large geode\nodule has a mostly unblemished exterior indicating it was likely not transported by water to location where found.

Photo 3097: This flat bottom rounded top geode with nearly pristine exterior, is not indicative of chipping and breakage by water transport.

Photo 3668: Multiple flattened bottom nodules in matrix do not line up on the same axis; hence, were deposited here randomly by a mudflow of ashy material and not actually formed in the ‘deep pit’.

Photo 3039: Were these variably sized geodes and nodules transported to the ‘deep pit’ by a mudflow without exterior damage or severe fracturing?

Photo 3803: This large blue banded agate geode has many sagenitic inclusions which, except for sagenitic iron ‘star bursts’, are not very common in the ‘deep pit’ geodes and nodules.

Photo 3088: This is a fortification agate nodule surrounded by sagenitic ‘star bursts’. These iron ‘star bursts’ are the only type of sagenites common in the ‘deep pit’ material.

Photo 3795: This blue banded agate geode has very few sagenitic inclusions which are, however, very common in geodes found over the last 12 years on the rest of The Carver agate field.

Photo 3191: This amethyst geode discovered where it did not belong beside the road, was the initial clue to what was to become the ‘deep pit’ mystery.