The Great Fresnoite Discovery

of 1998

 
 

"A Summer of Hard Work Brought Him Unbelievable Rewards"
by Scott Kleine, Great Basin Minerals

Originally Published in Rock and Gem Magazine, March, 1999

Photos by Scott and Harry Kleine, Bob Keller

Here I am finding a cabinet fresnoite specimen in Pocket Zone #1 at the Junnila property.

 

Introduction-

     The Junnila property, located in San Benito County, California, contains a little-known deposit that has previously produced only small amounts of benitoite, scattered fresnoite and a mix of crystalline zeolites. Over the course of the summer of 1998 I organized and operated a substantial, heavy-equipment mining operation on this property. This effort produced new pockets containing superb fresnoite crystals, the largest being 2.2cm. These are considered the finest-known examples of this rare and aesthetic species.

History of the Junnila Property-
     The Junnila property has been mined intermittently for the last several years. Liza Junnila and Bill Larson mined the top of the deposit with the use of a D-8 Cat. It was reported that approximately 500 benitoite specimens were found during that period. The first reported fresnoites were also discovered during this operation. (The quality of these remains unclear.) Other species, such as natrolite, joaquinite and analcime were also recovered. Anything of interest exposed by this work was quickly snapped up by participants in later fee-digging tours. Afterwards, the quality of the specimens found quickly diminished. Upon my first visit to the mine, in May of 1997, very little was to be found as the mine had not been in operation for years and the collecting areas were well picked-over. Some beautiful, multicolored fluorescent specimens of heavily included benitoite, albite and calcite could be collected, as well as some very rare, broken/contacted crystals of yellow and, even more rarely, pink fresnoite. But, overall, the trip was more of a scenic adventure than a specimen-producing trip. I felt, however, that the property had much more to offer if some significant new exposures could be made.

A fresnoite crystal shown under daylight above left, and fluorescing under shortwave UV light above right.

     Then, in the middle of October 1997, John Veevaert wrote to tell me about a surface pocket of small, fluorescent fresnoite crystals he had recently found there at night. Motivated by this information, I drove to Liza's house and asked her if I could go to the mine and collect. For a nominal fee, I was allowed in for a weekend.

     Once at the mine, I followed John's instructions, located the spot where he had made his discovery and began a concerted effort to expose more fresnoite. Halloween night I found a number of contacted, but colorful, fresnoite crystals with my shortwave, ultraviolet light. Some of these specimens had undamaged, though small, fresnoite crystals on matrix. I was elated!

     The next day I gave the mine a good going-over and realized that it had a lot more potential than I had first thought. Later that day, Liza visited me at the mine and, to my amazement, mentioned that the property was about to be put up for sale.

 

My Fresnoite mining project, mid June, 1998.

"Wow!" I thought. "What an experience it would be to own and mine this property myself!" After careful consideration, I sent a proposal to Liza. It was accepted. By the end of the year, all of the contracts had been signed and signatures notarized. I now had the full lease to my own fresnoite and benitoite mine!

Location and Geology-
    The Junnila property is located on a 300-acre parcel of deeded, private property. No unauthorized visits are allowed. Access is made by driving eight miles up the Clear Creek Recreational Corridor, off Los Gatos Creek Road, into the heart of the San Benito Mountains. The nearest towns--Coalinga and King City--are each about 40 miles away.

    The general region surrounding the property is composed of varying grades of serpentinized basalts, contact-metamorphic bodies and islands of Franciscan phyllites and schists. Several unique, highly mineralized deposits occur within a few miles of the mine.

    Of the 300 acres comprising the Junnila property, only a few actually contain the specimen-bearing deposit. This is hosted in a series of bedded Franciscan phyllites and schists, which have undergone several episodes of mineralization. First emplaced were the blue schist facies, which host benitoite, strontio-joaquinite and neptunite. This rock type occurs as extremely hard, tough, resistant dikes which break apart into log-shaped boudins.

    Some time later, a series of important geological events took place at the site. Along the southern edge of the deposit, a major strike-slip fault formed. This juxtaposed a huge body of serpentinized basalts next to the Franciscan phyllite-and-schist hosted deposit--the Franciscan rock types occurring as the footwall and the serpentinized basalts as the hanging wall.

    Although the circumstances of the fresnoite's formation are not yet completely understood, I have strong reason to believe that the fresnoite formed from fluids flowing up, along the scarp of the serpentine fault. A 2-foot-wide reaction boundary of clay alteration occurs along this zone, providing evidence of significant, hydrothermal-fluid flow and rock alteration in the geologic past. The titanium source for the fresnoite was derived from the serpentines along this reaction boundary. Only a single, heat-altered brown benitoite was found anywhere near these structures.

Specimen-Quality Species-

Analcime: NaAlSi2O6+H2O, Isometric: This species was widely abundant in the general vicinity of the fresnoite-bearing structures. It occurred most commonly as massive, white, semicrystalline vein-fill along tight structures within the phyllite beds. When these fractures opened up, beautiful carpets of sharp, lustrous, white, trapezohedral crystals were found--most being associated with fresnoite.

    In general, the larger the pocket, and the closer that pocket was to the serpentine fault zone, the better and larger the analcime crystals that were found in it. The color of these crystals ranged from gray to snow-white, while the luster ranged from dull to mirror-brilliant. The largest and best analcime crystals were located on the hanging wall of what I called the "Mother-Load Pocket." Partial crystals to 10cm were recovered, with the largest perfect crystals being about 6cm in length. Some gemmy crystals to 1cm were also found.

    Most of the fresnoite specimens had at least some crystalline analcime association. Strangely, about a quarter of the analcime collected fluoresced bright green under shortwave, ultraviolet light. An impurity was thought to be the cause of this phenomenon. A scanning electron microscope spectral analysis was used and detected anomalous amounts of cesium in these crystals. Whether or not these specimens have enough of this element in the analcime crystal lattice to be reclassified as the mineral pollucite is a question still under investigation.

Benitoite: BaTiSi3O9, Hexagonal: The Junnila property is now the second known occurrence of specimen-quality as well as gem-quality benitoite. The specimen-quality material occurs as clean crystals in natural, open cavities. On this property, two, distinct varieties of this species have been found. The first, and most common, type is the "stony" variety. These formed anhedral, lenticular grains ranging in size from 0.1cm to 2.5cm, and were been completely included with crossite. Blue-schist boudins containing this type of benitoite were only found at night, with the help of a shortwave ultraviolet light. Some of these boudins contain an impressive, 30-percent volume of this species, making it an important, rock-forming mineral.

    The second variety of benitoite formed within tight veins of white albite, also in the blue schists. In rare cases, natural, open cavities containing rich-blue, gemmy benitoite crystals to 1.5cm were recovered. These crystals were typically associated with etched, crystalline albite and traces of calcite. Even more rarely, strontio-joaquinite and neptunite were also found in association.

    Complete benitoite crystals were rare and usually displayed a complex, stepped habit--sometimes showing even more-complex, etched faces. The luster on these crystals ranged from dull to brilliant, while the color ranged from colorless to a beautiful, almost tanzanite-like, purple-blue. One crystal was recovered containing a flawless section of approximately 0.5 carats. Vugs of this variety of benitoite tended to be very fluorescent. They cavities contained several different minerals showing one or more fluorescent shades of light to medium crimson-red, sapphire-blue, yellow-brown, green, orange and violet. These were truly rainbow-colored pockets!

Fresnoite: Ba2TiSi2O8, Tetragonal: The Junnila property is considered the finest fresnoite-producing locality in the world. So it is easy to see why fresnoite is the most important species of this deposit. The fresnoite crystals collected ranged from 0.5cm to an impressive 2.2cm. Crystal habits varied from full, five-faced, simple tetragonal pyramids to tabular, tetragonal pyramids showing six primary faces, along with a number of other, smaller secondary faces. Full-pyramidal crystals were found much more rarely than those showing the more complex, tabular habit. Many of the crystals had a pleasing, two-toned color, displaying light to medium salmon-pink hues in the front pyramidal faces, trending into varying hues of honey-gold, yellow-gold and yellow-brown toward the sides and reverse/base of the pyramids.

    Pink fresnoite--especially specimens with the stronger tones--are among the very rarest of all colors for this species, and have been recovered from no other locality so far. Only a few gemmy crystal fragments were found. If cut properly, these would produce mere 0.12- to 0.25-carat stones.

    The sharpness of the fresnoite crystals varied. All tended to have at least some sharp faces nearest their uppermost parts. Luster varied from dull to a stunning mirror-brilliance. Highly lustrous fresnoites were rare, indeed. Less than a dozen good examples were found.

    Matrices on which the fresnoites perched tended to be crystallized analcime, with rarer occurrences of natrolite and stilbite. This combination of species made for very unusual, colorful and aesthetic specimens!

    Two notable, small cabinet specimens were found in Pocket Zone #1 (described at length later in this article), which had brilliant, snow-white, drusy analcime crystals with one or more gemmy, brilliantly lustrous fresnoite crystals. On a single piece the "Fourth-of-July" crystal--a unique, second generation of 2mm, full-pyramidal, gemmy, yellow fresnoite crystals grew on the faces of the main, 1.8cm crystal--giving it the appearance of a starburst. This crystal was not the largest I found, but it was, in my opinion, the most aesthetically pleasing.

    Six apparent interpenetration-twinned fresnoite crystals were collected in the Mother-Load Pocket. Five of these occurred as two, tabular crystals, partially interpenetrating in the form similar to that of a (lambda symbol). Only a single, full-penetration twin was found, with a form similar to an X. The largest, and best, of the (lambda symbol) twins was a superb, 2.1cm, sharp, bicolored fresnoite perched on lustrous analcime crystals. I called this specimen "The Great Fresnoite Twin." This piece also represented the largest, undamaged fresnoite which I collected on matrix.

Natrolite: Na2Al2i3O10+2H2O, Orthorhombic: Several types of natrolite were observed at the mine. Most common was the massive form, which occurred as white, semicrystalline vein-fill averaging about lcm in width. Massive natrolite-filled pods up to 10cm wide were also seen. This material was noted mostly along many of the cross-cutting structures of Pocket Zone #1. In a few unusual cases, tabular fresnoite crystals were seen completely frozen in these veins.
    The next most-common form was that of the gray-white, stubby, 2mm to 4mm, milky, terminated crystals, which formed during a late-stage mineralizing episode in what I called the "Mother-Load Pocket." These crystals were found sprinkled on the hanging-wall and footwall analcime crystals, as well as on the footwall fresnoites.

    The rarest--and, of course, most spectacular--form of natrolite at the mine, occurred as supergemmy, superbly terminated, thick, prismatic crystals of high luster and quality. I only found a few, select specimens of this generation. The largest of these was a single, detached prism, some 3cm long and 1.5cm thick, well-terminated and of unquestionable gem quality.

    Another specimen was found which displayed 1mm fresnoite pyramids sprinkled on part of a 3cm group of these pristine natrolite crystals. Also, a cabinet specimen from Pocket Zone #1 showed a very aesthetic 1cm spray of five of these crystals, well associated with a 0.75cm freestanding fresnoite crystal.

Neptunite: KNa2Li(Fe+2,Mn+2)2Ti2Si8O24, Monoclinic: This species was very difficult to find. I only located a few minor specimens, consisting of black, 0.51cm, terminated crystals. One of these was associated with benitoite. The species only appeared in the blue-schist portions of the deposit. Both examples were found in natural, open dilations, along tight, albite-rich veins.

Strontio-Joaquinite: Sr2Ba2(Na,Fe+2)2Ti2Si8O24(O,OH)2+H2O, Orthorhombic: Strontio-joaquinite was a very elusive species to find in well-crystallized examples. It was an unusual mineral, in that it was the only collectible species that occurred in both the fresnoite-bearing phyllites and benitoite-bearing blue schists. This species was most common in the heavily albitized blue schists.

    The best specimen-quality examples--possibly the world's finest--were found on the hanging wall of the Mother-Load Pocket. These crystals occurred as flat-lying to freestanding, brownish-green to yellow-green, translucent to transparent, dull to lustrous crystals, ranging in size from 1mm to 6mm. The best specimen had a 6-mm, doubly terminated, bipyramidal crystal growing out of phyllite host rock. Two other specimens showed excellent associations of this species with fresnoite and analcime.

Associated Species-


Actinolite: Ca2(Mg,Fe+2)5Si8)22(OH)2, Monoclinic: This species was found in only one mud-filled pocket. It occurred as 0.5cm, freestanding, acicular sprays on gray analcime.

Albite: NaAlSi3O8, Triclinic: This mineral generally occurred as 1-mm to 5-mm, crude, etched, white crystals and massive vein-fill within the blue-schist dikes. It was a possible indicator for other species, such as benitoite, neptunite and strontio-joaquinite. Some albite fluoresced shades of crimson-red under shortwave ultraviolet light.

Calcite: CaCO3, Hexagonal: In Pocket Zone #1, 35-mm, rounded rhombohedrons and scalenohedrons of calcite occurred, ranging in color from tan, brown and orange, to a fiery red. All of these crystals tended to be of only moderate luster.

    Calcite was also found in the blue-schist dikes. These occurrences tended to lack any sort of crystallization. All the calcite found fluoresced yellow-brown and phosphoresced yellow. One cabinet specimen recovered in Pocket Zone #1 had a very unusual association of 1-mm to 2-mm, rhombohedral, brown calcite crystals, aesthetically sprinkled on a freestanding, 0.75cm fresnoite crystal.

Galena: PbS, Isometric: This was the rarest of all the species identified at the mine. Only two verified examples were recovered, both from Pocket Zone #1. Each specimen showed an approximately 1-mm, cubic cleavage of fresh, metallic-silver galena, associated with fresnoite. This species was confirmed with the use of a scanning electron microscope.

Stilbite: NaCa2Al5Si13O36+14H2O, Monoclinic: This species was found in two unnamed mineralized fault zones off to the northwest of the Mother-Load Pocket--one of which was fresnoite-bearing. It occurred as fine druses of complex, white, satin-like crystals up to 2mm in length. A few specimens displayed prismatic crystals with simple, two-faced terminations.

    The finest stilbite found was a superb small cabinet specimen that had over a dozen, 2-mm to 7-mm, tabular, freestanding, undamaged, yellow fresnoite crystals perched on a fine druse of white, crystalline stilbite.

Tremolite: Ca2(Mg,Fe+2)5Si8O22(OH)2, Monoclinic: This species was located within the blue-schist dikes. It occurred as white, silky, fibrous, web-like mats in a few, nonspecimen-bearing cavities.

Replacements-


Calcite-Pseudomorphic-After-Aragonite: This material was very closely associated with fresnoite deposition. A complex, two-stage replacement of aragonite by calcite, and then epimorphing of brown quartz over the calcite, left groups of unusual, flat-lying to freestanding, radial bunches of these brown, acicular, nonfluorescent replacements. Some were aesthetically associated with well-crystallized fresnoite. Most examples found ranged from 0.1mm to 3cm in length.

    In one unique case, a lcm, undamaged, extremely elegant fresnoite crystal was found completely perched on a 0.75cm-wide spray of this material, all of which was growing out of a 2cm mass of white, crystallized analcime! Conclusive analysis of this material was made with the use of an x-ray defractometer and a scanning electron microscope.

Chrysocolla-Pseudomorphic-After-Copper: Yet another very unusual replacement was identified. This involved intricate loops and archways of 1-mm to 5-mm wire copper, which, later, were completely replaced by translucent blue chrysocolla. Unfortunately, due to the fragility of these replacements, few intact pieces survived the specimen-removal process. Approximately 10 complete matrix examples were recovered--all from Pocket Zone #1.

Pocket Descriptions-


    I located and collected at least seven significant fresnoite-bearing pockets at this site. Three of these occurred within the Mother-Load Pocket Zone, while the other four were located in Pocket Zone #1.

Pocket Zone #1 was discovered along an east/west-trending, high-angle structure. Upon its discovery, a series of natrolite-flooded cavities were observed, leading into parallel sets of open, analcime-lined, fresnoite-bearing pockets. Several small (3cm to 5cm) crystalline cavities were collected, along with four other significant pockets up to 20cm long and 3cm wide.

    This pocket zone had a rich assemblage of unexpected species, including: fresnoite; analcime; calcite-pseudomorphic-after-aragonite; chrysocolla-pseudomorphic-after-copper; galena; calcite; and gemmy-prismatic natrolite crystals. One fantastic cabinet specimen showed all of these species except galena, and fluoresced four different colors under shortwave ultraviolet light.

    Fresnoites from this pocket zone were of superb color and beauty. Crystals ranged from 0.2cm to 1.2cm, and had a very rich, two-toned color. Some crystals showed rich, salmon-pink hues. The largest matrix, pink-dominant crystal from this zone was 1cm wide and displayed excellent luster.

    While crystals were found detached from matrix, most fresnoite found on matrix had pleasing associations of white analcime. One pocket of full-pyramidal fresnoites up to 1.2cm was found within three feet of the serpentine-fault contact. Two superb cabinet specimens, along with a number of other fine examples were ultimately recovered from this rich zone.

The 2.1cm "Great Fresnoite Twin" Crystal from the Mother-Load Pocket.

The Mother-Load Pocket Zone occurred along a semiparallel, high-angle structure, only three feet north of Pocket Zone #1. By far the largest vug in this zone, "The Mother-Load Pocket", produced 80 percent of the best fresnoite recovered. This huge, lenticular 1-meter-long by 1.3-meters-high by 5cm-wide cavity produced one flat of topnotch, matrix fresnoite specimens. From this pocket, three fresnoite crystals were collected which met or exceeded 2cm--the largest an incredible 2.2cm! Two of these huge crystals were found off matrix and one amazing 2.lcm, twinned crystal on matrix.

    All of the fresnoites collected from this pocket occurred as detached crystals, thumbnails or small cabinet specimens. Sorry to say, no true cabinet specimens were found. Specimens with three or more fresnoites on matrix were recovered, along with some that had up to eight! The most unusual fresnoite specimen observed in this immense pocket consisted of six interpenetration-twinned crystals.

    Most of the fresnoite specimens occurred on the crumbly, heavily brecciated footwall and were coated with stubby natrolite crystals. Only four examples were found on the hanging wall, all of which had excellent associations of large analcime crystals and/or strontio-joaquinite. It was interesting in that the analcime crystals on the foot wall were much smaller and lower-profile than those on the hanging wall. The only other material found was calcite-pseudo-aragonite.

My Mining Project-


My Father, Harry Kleine, collecting in rich, fresnoite bearing structures in Pocket Zone #1.

    Once I had the lease to the property, I had a lot of work to do! I had to find a good backhoe to rent and get people signed up for collecting tours. My dad pitched right in and bought an inexpensive, portable tent-trailer, made a kit for an outhouse and found a table, chairs, water jugs, gas cans and all of the other amenities of basic life needed for a three-month stay in the desolate, though scenic, San Benito Mountains.

    Finally, the time came. I drove to Fresno and rented my new Case-580 backhoe. I had a Low-Boy rig to take it up as far as the driver could go, and then walked it up the last eight miles of dirt road to the property. My dad towed the tent-trailer with a truck he got specifically for that task. It was a tough trip up to the mine, and I had to pull my dad's truck out of a few holes with the backhoe. But by the end of the day we'd made it! Once we'd arrived, Dad immediately began to set up camp, while I went right to work, using the backhoe to make a series of fresh exposures in the deposit, in preparation for the upcoming Memorial Day collecting tour. I carefully scraped away the loose muck and exposed the long-buried specimen-bearing rock underneath. This was a dream-come-true moment for me: a goal I had worked toward diligently for six months!

 

Fee digging activities during May, 1998.

    On Memorial Day weekend, 15 people came up for the initial fee-dig. On the very first night of collecting, a beautiful fresnoite pocket was discovered. This was a good sign, as I had barely scratched the surface of the deposit. It also made for a good, first fee-dig tour. At that moment, I felt that all of my original intuitions about this deposit had been right on!

    Within the first two weeks, as I continued work on the first six-foot-high bench wall into the deposit, I began hitting small pockets of contacted, but colorful, partial crystals of fresnoite. As the days went on, the pockets grew increasingly larger, until I discovered a 15-foot-long string of separate, high-quality, specimen-bearing fresnoite pockets. This area was christened Pocket Zone #1.


Mining along the serpentine-Franciscan fault boundary.

    As I continued to mine this zone, the quality of the fresnoite sharply declined when I drew within a few feet of the serpentine fault. At the contact of this massive structure, all traces of fresnoite mineralization vanished.

    Concerned about where to go next, I spent two days removing all of the surface muck from the floor of the pit, where Pocket Zone #1 used to be. I persistently cleaned a 10-foot by 15-foot surface area, until the white analcime and natrolite structures were clearly presented out of the dark-gray phyllitic host rock.

Mapping the floor, where Pocket Zone #1 used to be. Red flags indicate exposed fresnoite pockets. The yellow arrow points to the yet-to-be discovered Mother-Load pocket, a mere 2 feet below this surface.

    I then coordinated with AZCO, a Canadian mining company which happened to be concurrently sampling the Gem Mine, just a few miles away. I found the staff very friendly and willing to help me with my mapping needs. I arranged to have the 10-foot by 15-foot fresnoite zone mapped at a 1-to-24 scale, and the whole deposit mapped at a 1-to-240 scale.

    The interpretation of the resulting maps led me to a localized zone of concentrated fresnoite mineralization. Using the backhoe to trench alongside this zone and, subsequently, working carefully by hand over to the zone, I exposed an incredible 3-foot-high wall of 2-inch analcime crystals! This was the beginning of "The Mother-Load Pocket"! This was a very exciting time of discovery!

    After digging vertically through the Mother-Load Pocket for almost 8 feet, I came across a crumbly, brecciated pocket of loose analcime crystals coated with rich black soil. One of the first pieces I picked up looked like most of the others in the pocket. But, as I hefted it, I noticed that it had an unusually high density. I raced to the camper and washed off what I immediately dubbed "The Fourth-of-July Crystal"!

The "Fourth-of-July" Crystal, 1.8cm, from the Mother-Load-Pocket Zone.

    Within a few days, all of the specimen-bearing ground had been very thoroughly collected and I backfilled the hole where the Mother-Load Pocket Zone had been, ending collecting at this site.

    By now it was the end of June. Over the next three weeks, I began a long period of serious rock-moving, pulling one 5,000-pound to 9,000-pound blue-schist boulder after another out of the solid dikes. It was grueling work, as the temperature was over 100 degrees every day.

    I would occasionally find a boudin that contained some stony benitoite, but little else. I continued to push the bench northwest, until I had worked completely through the deposit. It was now the middle of August, and time to tear down our camp, drive the backhoe out and go home. Reflecting back, I realized that I had the privilege of making over 50 new friends who had come by for my fee-digs.

Specimen Preparation-
    When I got home, I immediately began the process of cleaning and trimming all of the fresnoite I had collected. I soon realized this was going to take a lot of time and energy. Many of the best specimens from the Mother Load Pocket had a heavy coating of late-generation natrolite, which had to be removed. But after studying up on my cleaning agents, I found that fresnoite, analcime and natrolite were all soluble in most acids. After a lot of testing, I discovered that, by selectively waxing the analcime matrix and only leaving the natrolite-coated fresnoites exposed for brief periods in dilute, semisaturated HCl, the natrolite could be safely removed from the fresnoite crystals.

    Other specimens had very hard clay stuck to them. I learned--much later--that this coating would only come off after months of soaking in pure, pH-stabilized water, with regular ultrasonic cleaning cycles and a lot of elbow grease. But I found it a pleasure to work with these rare, aesthetic specimens of high quality, to expose their optimal natural beauty.

Conclusion-
    My mining operation at the Junnila property produced a number of world-class fresnoite specimens. Other species, which were also found, turned out to be much more varied and unusual than I had first imagined. I wonder if any future mining on the property will result in more significant mineral finds.

I hope this account of my experience will inspire you to try your hand at mining. Good hunting!

Scott Kleine      Reno, Nevada


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