BADGERS, STONEHENGE, AND A FURSTY FERRET

THE EUROPEAN BADGER, MELES MELES.  PHOTO COURTESY OF BBC.

 The big news from Maidenhead, UK, (see previous post) centers around badgers.  Yes, those ornery furry members (Meles meles) of the weasel family.  It appears that a substantial number of people believe the boogers need culling (a nice word for killing).  Another substantial number of citizens love the critters.  A fight is brewing!

I learned that UK cattle have a serious problem with bovine tuberculosis—to the tune of tens of thousands of cattle being slaughtered at a large monetary cost to the farmers.  As with many personal financial losses, there is a tendency to fix the blame on an external force rather looking to an internal cause.  Bovine TB is a nasty disease and in most other countries farmers slaughter an entire heard to prevent its spread.  However, in the UK farmers tend to slaughter only a single infected animal.  That leads us to badgers!  It seems that cattle can infect badgers and vice versa with the disease.  So, the obvious answer to many people is, wait for it, shoot most of the badgers.  But the badgers are quite prolific breeders this year and have vastly increased in numbers.  And those of us who have lived in the Midwest know that unlimited shooting of deer in areas of chronic wasting disease was about as successful as a lead balloon.  So, the argument goes on and on—to shoot or not to shoot.   The problem has reached the highest level of the government and Prime Minister Cameron has now postponed the culling—kicked the can down the road.

In my previous post I lamented about the lack of outcrops in the Thames River basin near Maidenhead.  Perhaps I just missed the rocks, or they were obscured by the vegetation, or maybe modern construction activities destroyed the evidence.  At any rate, I needed my fix of rocks and so begin hunting for areas external of the town.  Well, we located some fascinating rocks; however, they were exotic to the area and not arranged in stratigraphic order!  On the other hand, these rocks were located at a World Heritage Area the world knows as Stonehenge. 

THE STONE STRUCTURES AT STONEHENGE.

We decided to brave the traffic and head west from Maidenhead driving “on the wrong side of the road” for about 70 miles to near the village of Amesbury.  Other than some white knuckle stress the trip was completed without incident.  I do feel fortunate that this excursion was completed midweek in October rather than in prime summer visitor season.

Millions of people around the world have at least heard of Stonehenge, mostly due to these very large rocks laid out in a mysterious arrangement.  There is some sort of stone alignment with the sun and the Summer and Winter Solstices are special times.  However, we (modern populations) often fail to understand that some members of past civilizations were “very intelligent” and were able to interpret and predict celestial events with great accuracy.  These events were marked in a variety of ways including rock windows, stone markers, displays on rock faces, etc.  At Stonehenge the builders marked these celestial events by importing some really large rocks, some as large as 25 tons, and arranged them in a methodical order to maximize astronomical observations and mysticisms. 

A PLACE OF REVERENCE AND MYSTICISM.

The more I tried to learn about the history of Stonehenge, the more confused I became!  However, that seems normal as scientists have been unable to unravel but a small part of the history.  Media outlets have popularized the pagan ceremonies of the modern neo-Druids at Stonehenge, and equated these activities with ancient Druids.  In doing so, they have piqued the interest of the public.  However, the British Museum believes neo-Druids have no connection with ancient Druids, a group of priests living in the UK and France before the arrival of the Romans. And, Stonehenge was long constructed before the ancient Druids obtained any sort of power in the population.

The history of Stonehenge is complex and certainly beyond the scope of this posting. So, I encourage readers to locate some of the hundreds/thousands of articles and books written on the subject—just carefully scrutinize the sources and stick to reputable authors such as the British Museum and academic geologists, historians, and archaeologists. 

Stonehenge, at least what remains, is a circular placement of large exotic rocks arranged within a series of ditches and earthworks.  Although unique in several ways, it is far from being the only example of ancient works.  There are literally hundreds of Neolithic (~4000-2500 BC) and Bronze Age (~2500-800 BC) rock works, rock monuments, and burial mounds located in the UK.  The earliest evidence of human activity at Stonehenge dates to perhaps ~7500-8000 BC and is in the form of holes that held posts (that would be postholes!).  What these poles held up seems to be anyone’s guess. The earliest rock construction seems to be ~3100 BC and involved digging a ditch, and piling up the rocks, in the poorly exposed chalk bedrock (Cretaceous Seaford Chalk).

PERHAPS THIS WAS STONEHENGE?  SKETCH FROM MANDALASROK.COMUF.COMJ.

By around ~2600 BC the builders were using an igneous rock (Ordovician dolerite/diabase) locally called bluestone, and lesser amounts of rhyolite and tuff.  The original source of the bluestone was from Wales, and scientists have long debated the mechanisms of transporting large (several tons) rocks over 150 miles.  Recently workers from the British Museum have suggested the bluestones were actually taken from local glacial erratics—still from Wales but transported to a closer location by Pleistocene glaciers.  

A major building phase from ~2600-2400 BC produced perhaps the most impressive part of the Stonehenge structure—construction of a ring of 30 standing rocks (each 13 feet high, 7 feet wide, 25 tons) capped with 39 “lintel” rocks (10 feet by 3.5 feet)—the so called Sarsen Stones!  These rocks, a silicified Tertiary sandstone, came from quarries perhaps 25 miles distant, or from local glacial erratics.  Inside this circle is a U-shaped arrangement of five “trilithons” (two standing rocks topped by a lintel) held together by a mortise and tenon joint system.  Inside of this arrangement are other rocks including the “alter stone”.

HOW DOES ONE MOVE MULTI-TON LINTEL STONES TO REST ON THE UPRIGHT STONES?

Additional building, and rock rearrangement, of Stonehenge continued for several hundred years, and modern civilizations have contributed to its demise by “taking away” bits and pieces and even whole rocks.  Today Stonehenge is owned by the Crown and surrounding land is protected by a trust.

THE HEELSTONE, COMPOSED OF SILICIFIED TERTIARY SANDSTONE, IS NOT LOCATED WITHIN THE STONEHENGE CIRCLE.

Theories abound as to the use of Stonehenge—take your pick.  Was it a cemetery? Yes, at least part of the time.  A place of mystical or spiritual worship?  Probably.  A place for astronomical observations?  Yes, at least part of the time.  A place for healing?  Maybe, that is a recent proposal. Whatever its use, the builders and users left behind no written record and Stonehenge’s place in history may always be debated.  However, we found it to be a place of marvel and reverence. 

A COOL FURSTY FERRET AFTER A WHITE KNUCKLE DRIVE.

Upon returning to Maidenhead I poured myself a pint of Fursty Ferret and tried to interpret what I had seen—it was confusing!   However, I could picture in my mind a group of ancient people gathering at Stonehenge trying to decipher the events of a Summer Solstice.  

ADDENDUM SEPTEMBER 27, 2013 FROM THE BBC:

A badger cull is under way in England despite protests, the National Farmers' Union has confirmed.

About 5,000 badgers are expected to be killed in controlled shootings over six weeks in Somerset and Gloucestershire.
Supporters say the cull is necessary to tackle bovine TB, which can be spread from infected badgers, but opponents say it is inhumane and ineffective.
 

OLD THUMPER & THE THAMES RIVER

THE RIVER THAMES AT MAIDENHEAD.

For the last several days I have been searching for rock outcrops, any type of rock and any outcrop--without success! I need to get my daily fix of "rocks" but alas I have settled for looking at the paving stones (granitic) and ornamental "gravel" (slate). However, there are other interesting items that make up for the lack stratigraphic sections.

My spouse and I are visiting our son and family in Maidenhead, UK, a town west of London and very near the famous Windsor Castle, home of the Queen. The last time I looked her standard was flying (she is home) and I thought about stopping in for tea. Right now my major project is inquiring about the native rock used to build the massive castle. All of the sources available to me at this time  refer to the construction material as "stone". But, is that a quarried rock of some sort, dressed river cobbles, or perhaps brick?  Don't know.

THE BRIDGE AT MAIDENHEAD. 

Maidenhead is located on the River Thames upstream from London about 26 miles and their town bridge dates from 1777. This river is certainly the most famous stream in the UK, and is also the longest river flowing entirely in England---215 miles. Much like the Mississippi River in the US, the Thames has a disputed marked source (seasonal springs at Thames Head) in west-central England and generally flows east finally emptying into the North Sea via the Thames Estuary. The River is wide and tidal from the Estuary until a few miles upstream of London (Teddington Locks).  It is the major shipping lane for the Port of London and the Royal Navy steamed an aircraft carrier to dock during the recent Olympics.  Although a proto-Thames drainage was established perhaps by ~60 Ma, the current river owes its course to Pleistocene glaciation.

Through Maidenhead the river is navigable, but is quite narrow, and the barges and boats seem long and very "slim". I am uncertain how some of the boats are able to "turn around" in the river!  A couple of days ago I walked up to the local locks, the Boulter's Locks (current locks date to 1828), and observed locking through. They are quite tiny compared to the massive locks on the Mississippi River near my former home in Wisconsin.

                                                               BOULTER'S LOCKS.

We have been driving a daily trip, about 10 miles RT, on "the wrong side of the road" but now have our "left side curb bumping" down to about one per day. The secondary roads are quite narrow, very sinuous, and most are curbed. I seem to have trouble on one particular curve where the width of each lane is 6.5 feet. Cars are able to park, in many instances, on both sides of the road pointing in either direction. So, you are traveling down the road trying to stay left and notice a car on your side pointing toward you. Nothing to worry about for the normal English driver as the car is simply parked. However, that aspect is always worrisome for me, a novice driver! In addition, our daily route includes several one lane bridges where certain directions have priority driving across. There seems to be numerous " light flipping events" as a way of saying thank you for letting me drive through.

We enjoy walking downtown in the mornings to have our daily libation at Java and Company. All coffee, as best I can tell, is served Americano style and with steaming hot water poured over 4 shots of espresso in a ceramic mug (take-away paper cups are not common). The coffee is HOT but no one here would think of suing the shop. I also have a soft spot in my heart for sweet pastries so am able to get my daily shot of sugar in the shop!

                                                     MAIN STREET, MAIDENHEAD

Morning coffee is always good with a newspaper and as a news junkie I am enjoying the selection of papers. It is quite easy to find at least 10 dailies to choose from. I sort of prefer the Daily Express at 5 pence, about $07.5. What a bargain.

Main street Maidenhead is a polyglot of smells and people and activities. I had an interesting talk with an ancient Sikh the other morning on a park bench and watched the street buskers perform their acts. The street is blocked off to traffic and several days per week, at least this time of year, there is a Farmer's Market spread out. Some of the veggies and fruit are local products while others are from Spain and Italy--I learned that tidbit from the Cockney vendor and who constantly called me mate or guv, and my spouse "darlin".

The UK is "sort of" part of the European Union as they maintain their own currency (British Pound Sterling) but participate in most other ways. However, there seems to be quite a push by many members of parliament to remove the UK from that organization. It will be interesting to see the results---if the government allows a vote. Another major issue coming up is a vote by Scottish citizens to become an independent nation and leave the UK (England, Wales, Northern Ireland, and Scotland).

                                           ONE FOR EVERY NIGHT OF THE WEEK!

I am also fascinated by the advanced age (at least according to U.S. chronology) of the buildings. One of the local pubs in nearby Bray was constructed in the 15th century and others are older. And speaking of pubs, it is a treat to visit the local establishment for a pint of ale (my favorites are Fursty Ferret, and Old Thumper (A Beast of a Beer) and conversation. To my great happiness, 8-10 televisions are not blaring out football games during visits.  Over the weekend we went in for the Sunday Roast and part of the fare included Yorkshire Pudding.  At other visits, the bangers and mash were gourmet--but lots of calories!  After a couple of visits, the pub locals were quite accepting of strangers.

Unfortunately I have not been able to locate a local rock/mineral shop nor a local rock and mineral club. I had been hoping to acquire some new like-minded friends!  On my next trip I will probably attempt to find a local club outside of the immediate Maidenhead area, but that is another story.

mike

SPHENE: A NICE GEMSTONE

BEAUTIFUL GREEN AND GEMMY SPHENOID CRYSTALS, SOME TWINNED, OF TITANITE WITH GEMMY PORCELAIN-WHITE ORTHOCLASE VAR. ANDULARIA.  WIDTH ~3.8 CM.  COLLECTED TORMIQ VALLEY, GILGIT-BALISTAN, PAKISTAN.

I grew up in geology classes with the name "sphene" firmly entrenched in my repertoire of mineral names (CaTiSiO₅).  I really didn't know too much about the mineral except that study collection housed a really nice greenish crystal.  During those halcyon days of my youth I believed that all crystals in the field certainly would be almost identical to those specimens in the study collection!  Wow, that thought was one of those "non-truisms  they teach you in school" moments.

   

Later on in sedimentary geology class I discovered that sphene is classified as a "heavy mineral" (specific gravity 3.5+ for sphene) and may be separated (for example in sandstones), along with other "heavies" such as zircon, ilmenite, epidote, apatite, magnetite, garnets, rutile and others.  An analysis of these heavy mineral concentrations often help geologists understand the original source area for the particles in the sandstone--many heavy minerals are distinctive of a specific source area.  For example, one class project determined that the provenance for a particular sandstone was a series of metamorphic rocks a few hundred miles away---the abundance of rutile in the heavy mineral separation lead to that speculation.  Rutile is a common mineral in high temperature-high pressure metamorphic rocks.

Heavy minerals (density greater than ~2.9) may be separated from "lights" (such as quartz and feldspars) by the use of a heavy liquid such as bromoform and a centrifuge.  Further separation may be made with the use of magnetic attraction.

Rockhounds are quite familiar with mining of placer gold.  However, several other minerals form important placer deposits such as the titanium-rich ilmenite beach sands in Alaska. Cassiterite placers are important sources of tin in Malaysia and Indonesia.

Sphene is a common accessory mineral in many igneous and metamorphic rocks; however, the grains are usually small and tough to distinguish with a hand lens.  But, with the use of cut thin sections and a petrographic microscope, a whole new world opens up for the geologist.  Sphene is observable and identifiable.

My next experience with sphene occurred in the shop of a faceter who had stunning specimens of this green to yellow-green, high dispersion, gemstone.  However, these faceted specimens are mostly for exhibit since their hardness is quite low (~5-5.5) and the mineral is brittle and easily breaks.

I now look for sphene stones to examine; however, they are often tough to locate.  The faceted stones have a brilliant luster, some unique colors of green to yellow-green, and maybe even tending to a brownish-green or reddish-green.  In fact, the stones, if cut correctly, exhibit a nice pleochroism-changing colors when looked at via different angles.  A jeweler told me that some of his faceted specimens have a very strong fire especially when displayed with a brilliant cut (refractive index of over 2).  Although I have not seen such, it is my understanding that heat-treated stones will lose their "greenness" and turn red.

So, I have seen many "grains" of sphene via heavy mineral separation and thin sections but was still on a quest for one of those nice green crystals! Where would I find one?  Well, the specimen finally came to me via an unexpected route--in a flat of mixed minerals at an estate auction!  Whatever, I now have these beautiful green crystals--of titanite?  Yep.  Seems like in 1982 the International Mineralogical Association Commission on New Minerals and Mineral Names adopted the name titanite and discredited the name sphene (for its wedge shaped crystals) since the mineral has a high percentage of titanium (CaTiSIO₅).  How could they do such a thing?  RIP sphene.

mike 

Post Script: I recently was able to acquire another crystal of titanite collected from Kennesaw Mountain, Georgia.  It is perched, by itself, on a mass of quartz.

WIDTH OF CRYSTAL ~.88 MM.

 

COLUMBITE & TANTALITE

I am often confused about identification of minerals in the Columbite-Tantalite series; of course numerous other ideas offer confusion to my mind!  As I understand the situation, columbite (Fe, Mn)(Nb,Ta)₂O₆ [niobium-rich] is in a solid solution gradation with tantalite Fe,Mn)(Ta,Nb)₂O₆ [tantalum-rich) and individual specimens are very difficult to accurately name (without some sophisticated instrumentation).  In fact, pure end members may be rather rare in nature.  The amount of manganese also varies in the specimens. The best bet for field identification seems to be the high specific gravity, (~7.9) for iron-rich tantalite, compared to ~5.3 for columbite.  Both have a subconcoidal fracture, good cleavage in one direction, black to brownish-black color, and a submetallic luster.  Add that to the note of  www.MinDat.org: iron-tantalite is fairly rare and many specimens are actually misidentified as iron-rich tapiolite (tetragonal dimorph of Fe orthorhombic tantalite).  With that in mind, I am uncertain what an ole stratigrapher like me is suppose to do? 

   

Columbite-Tantalite is often found in lithium-and phosphate-rich pegmatites and associated with such minerals as spodumene, beryl and lepidolite.  Mining of these minerals is ongoing as tantalum is used in the manufacture of electronic capacitors.  Niobium has uses in strengthening iron alloys, and in superconducting medical magnets.  Brazil, Australia and Canada seem to be the major producers of tantalum and niobium at the current time.  However, in past years the pegmatites of the Black Hill in South Dakota have produced many tons of the minerals.  Roberts and Rapp (1965)  state:  "The Black Hills have received world-wide recognition for the many excellent specimens of columbite-tantalite collected from pegmatites in the area since first reported in 1884...In addition to specimens, over 65 tons of columbite-tantalite have been produced since 1918 as a by-product of mining other minerals".  I am unaware of current mining for columbite-tantalite in the Black Hills.

TWINNED PARTIAL CRYSTAL OF TANTALITE.  WIDTH ~2 CM.

  I have a small specimen of "columbite-tantalite" collected many years (decades) ago from somewhere near Custer, South Dakota.  At times in my life, especially when younger, my note taking and locality information was not the best; I thought my memory would last forever!  I know this specimen came from near Custer and my best guess is the Tin Mountain Mine west of the city.  The specimen is a section of a twinned crystal and actually is pretty nice.  My guess is that the mineral specimen is an iron-rich tantalite (rather than columbite) since the specific gravity (heft) seems high.  At the Tin Mountain Mine Precambrian metamorphic rocks, mostly a schist, host the zoned pegmatite.

 COLUMBITE CRYSTALS SET IN CRYSTALLINE QUARTZ.  LENGTH ~7 CM.

My second specimen from the columbite-tantalite series was collected closer to home, somewhere west of Colorado Springs.  I purchased this specimen from an out-of-state rock/mineral shop so only have the following information: "Tantalite, St. Peter's Dome, CO".  The specimen exhibits  massive blocky  "slabs" of the mineral surrounded by crystalline quartz.  I suspect the mineral is columbite since Eckel (1997)     stated, "Columbite is probably more common that tantalite in Colorado because of the limited degree of differtiation of the host granites and pegmatites...The earlist reported occurrence of columbite in the state was from Pikes Peak, possibly the Crystal Park or Stove Mountain areas."  Since Stove Mountain is near St. Peter's Dome perhaps the specimen in my collection was mislabeled since the "Dome" is much better known.

MT. ANTERO: HELIODOR & EUCLASE

MT. ANTERO, 14,269 FEET.

Mt. Antero, and neighboring Mt. White, are two of the more spectacular mineral collecting sites in Colorado, and in fact, in the entire U.S. Collectors, both amateurs and professionals, have been chasing beryllium minerals, but especially aquamarines, for decades (at an elevation exceeding 13,000 feet). 

Several years ago, after first arriving in Colorado Springs, I purchased at auction a bucket of material with an included note labeled "Mt. Antero".  It appeared that the material had been screened since the largest size particles were no longer than about 1.5-2.0 cm.  At any rate, I had not been to the Mt. Antero collecting sites at that time so decided that the bucket should be mine.

Like many good projects, time became a factor and I simply let the bucket languish in a garage storage area---until this fall!  One day I found the bucket, took a quick look, and decided that I needed to do some picking.  The results were: numerous small aquamarine fragments [a blue variety of beryl: Be₃Al₂(SiO3)₆], fragments of goshenite [clear colorless beryl], a few small phenakites [Be₂SiO₂], goethite after pyrite cubes, some terminated quartz crystals, lots of broken "milky" beryl and feldspar fragments, and a couple of very interesting specimens.

One surprise find was the appearance of a small broken crystal of heliodor, or yellow beryl.  As I understand the situation at Mt. Antero, heliodor is not all that common. This crystal is certainly not a gem piece as fractures and etching are abundant; however, it is an interesting find.  The yellow color seems due to the presence of Fe+++ (ferric iron).

 

SMALL PARTIAL CRYSTAL OF HELIODOR.  LENGTH ~ 1 CM.

 

The second surprise was a colorless, striated, "flattened", prismatic crystal with one end terminated.  I did not have the slightest idea about what name to give this enigmatic specimen.  So, I begin a search for minerals that might occur with beryl ruling out other clear minerals such as phenakite, quartz, topaz, fluorite, and bertrandite.  Finally, I examined the "Mt. Antero" section of MinDat.org and looked closely at the mineral photos.  Thus, I came upon a single photo of euclase and "hit the winner".  Although it appears to be rare at Mt. Antero, it has been collected and photographed.  I am far from a mineralogist; however, the distinctive shape of the prismatic crystal, along with the striations, have been imprinted in my mind!



 

TERMINATION OF EUCLASE CRYSTAL. WIDTH ~9MM.

 

I suppose euclase should not be unexpected since it is a beryllium mineral [BeAl)SiO₄)(OH)] and closely related to beryl.  In fact, euclase is the product of decomposition of beryl.

Any day collecting at Mt. Antero is a bonus day in your life and does not count against your life span!  Just be aware that numerous active claims exist, and afternoon storms, including lightening, are a distinct possibility.  Flatlanders should always acclimate themselves at a lower elevation before attempting the assent.



 

mike

CALCITE FROM LA GARITA

The San Juan Mountains are known to most geologists as a volcanic terrane since there is a tremendous amount of evidence pointing to numerous volcanic eruptions in the Tertiary (last 66 million years or so). The San Juan’s are also home to perhaps 60 volcanic calderas, usually circular or oblong collapse features indicating ancient volcanoes that “blew their stack”.  The largest of these features is known as the La Garita Caldera, a truly gigantic structure.  Ort (1997) estimates the caldera was approximately 22 X 45 miles in size and produced about 5000 cubic-miles of volcanic material.  The pyroclastic ejecta generally are referred to the Fish Canyon Tuff (a silica-rich quartz latite containing about 40 per cent phenocrysts) that was scattered over a wide area with wind-blown ash perhaps reaching the east coast of the U. S.  There is a radiometric date of 27.8 Ma (Tertiary: Oligocene) on the rock unit (Ort, 1997).

 THE SAN JUAN VOLCANIC FIELD.  MAP FROM BACHMANN AND OTHERS, 2002.

The eruption of the La Garita Caldera is related to the Mid-Tertiary Ignimbrite Flare-Up, a period of very explosive volcanism centered in Nevada, Utah and Colorado approximately 25-40 Ma (Cannon, 2002).  In fact, the San Juan Mountains are the result of several of these volcanic explosions producing both lava rock (basalt) and pyroclastic rocks like ash and tuff.

 

  FISH CANYON TUFF, SAGUACHE COUNTY, COLORADO.

Since the initial blowout of the Fish Canyon Tuff, Carter (2009) has described seven additional eruptions seemly clustered near the center of the La Garita Caldera.  One of these eruptions created the Bachelor Caldera and spewed out the 190 cubic-mile Carpenter Ridge Tuff.  About 27 Ma an explosion created the San Luis Caldera and ejected the 135 cubic-mile Nelson Mountain Tuff.  At 26 Ma the same volcano created the Creede Caldera that expelled the 120 cubic-mile Snowshoe Mountain Tuff.

The Crystal Hill Mining District is located a few miles north and west of the community of La Garita near Carnero Creek.  The District was founded in 1881 by prospector and mining man Mark Biedell.  Crystal Hill produced native gold and silver from a collapse breccia structure for a few years before mining operations ceased, mostly by 1900.  Two small, short-lived mining camps sprang up in the area. The first, Biedell, appeared in 1881 and 1000 men were mining by 1883; the second sprang up in 1886 and was known as El Carnero (GeoZone, 2011).  The latter area was producing from “lead carbonate” (BLM information sign), a mineral I presume is cerussite (PbCO₃).  Eckel (1997) did not mention cerussite at Crystal Hill but did note its occurrence at the Bonanza District about 30 miles away: “…cerussite followed angelesite and covellite as shells on massive galena.”  

In the 1940’s mining evidently returned to Crystal Hill in the form of the Crystal Hill Mining Company (BLM information sign); however, I was unable to locate additional information about this later activity.

Voynick (1994) noted that “exploration geologists returned to Crystal Hill in the late 1970’s, delineating a large, low-grade zone of disseminated gold near the top of the hill.  The Crystal Hill Mining Company developed an open-cut heap leach mine recovering 30,000 troy ounces of gold in four years”.  In 2009?  U. S. government “stimulus funding” allowed the BLM to reclaim, at least partially, the old mine.  BLM now allows access on the reclaimed area but warns that the main pit is off limits and is situated on private land. 

   SLENDER TERMINATED QUARTZ CRYSTALS FROM THE CRYSTAL HILL MINE. WIDTH ~ 4.2 CM.

The Crystal Hill Mine is best known for producing terminated quartz and amethyst crystals and I wrote about these specimens in a posting on November 19, 2011.  However, another interesting specimen mineral coming from Crystal Hill is aragonite/calcite.  Voynick (1994) described the crystallization process as: “The last solution [a high-silica solution] which leached downward from the surface carried calcium carbonate from dissolved limestone.  The silica crystallized as drusy quartz and, in vugs, as well developed crystals of clear, smoky, and amethyst quartz crystals…  The dissolved limestone recrystallized as white needles of drusy calcite.”

 

  CALCITE CRYSTALS OVERLAIN BY GLOBULAR ARAGONITE. WIDTH ~ 5 CM.

My Crystal Hill specimen has scalenohedron calcite crystals overlain by rounded aragonite and is quite impressive.  John Betts (John Betts Fine Minerals) states that the aragonite fluoresces green and the calcite fluoresces blue-white under UV illumination.  However, I have neither a short-wave nor long-wave lamp to check this statement.

REFERENCES CITED

Cannon, E., 2002, The Mid-Tertiary Ignimbrite Flare-Up: www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/ignimbrite_intro.html.

Carter, J., 2009, La Garita: the World’s Largest Eruption: AssociatedContent,  www.associatedcontent.com/article/1001330.

Eckel, E. B., and others, 1997, Minerals of Colorado: Golden, Fulcrum Publishing.

GeoZone, 2011, The Lost Mine of Saguache Creek:
www.thegeozone.com/treasure/colorado/tales/co014b.jsp#prospecting

Ort M., 1997, New Results for the 27.8 Ma Fish Canyon Tuff and the La Garita Caldera, San Juan Volcanic Field, Colorado: Commission on Explosive Volcanism,
http://staff.aist.go.jp/s-takarada/CEV/newsletter/lagarita.html

 Voynick, S. M., 1994, Colorado Rockhounding: Missoula, Mountain Press Publishing Company.