RIEBECKITE; AN INTERESTING MINERAL

MASS OF RIEBECKITE FROM MOUNT ROSA GRANITE.  NOTE INDIVIDUAL COLUMNAR CRYSTALS.  WIDTH OF SPECIMEN IS ~4 CM.

For decades I explained to students and laypersons that the common rock termed “granite” had an easy mineral identification:  about 20% or more quartz, 60% to 80% feldspar (both alkali types such as orthoclase, and plagioclase), and a dark mineral such as biotite and/or hornblende.  There are numerous varieties of granite but all contain either hornblende or biotite.  Wrong!  I just needed to move to Colorado and discover the Precambrian Pikes Peak batholith.  In addition to the biotite-hornblende myth, I thought that the Pikes Peak Granite was just a “big ole pluton” with a fairly homogeneous mineral composition and generally pink in color; the pegmatites present contained larger crystals.  Wrong again!

Smith and others (1999) pointed out that the Pikes Peak Batholith is a composite system (~1.08 Ga) composed of at least two different granite types.  The first is a “potassic” series (~64%-78% by weight of SiO₂ with biotite and or hornblende), mainly the “real” Pikes Peak Granite, and a “sodic” series (44%-78% SiO₂).  Rocks of the latter series were emplaced via at least seven different smaller plutons, among them the Mount Rosa Granite.  Both of the “series” were emplaced close together in time and space although the Mount Rosa Granite has been intruded into the Pikes Peak Granite (Gross and Heinrich, 1965).  

Near St. Peter’s Dome on the flanks of the Pikes Peak Massif, the Mount Rosa Granite crops out, and its major minerals include microcline feldspar, quartz and riebeckite.  So here, the major dark-colored silicate mineral in the granite is the somewhat rare amphibole, riebeckite (Gross and Heinrich, 1965).  Although most of the Mount Rosa Granite is fine grained, some pegmatites are present (see specimen photo).

Riebeckite is an iron-sodium silicate [Na2][Fe²⁺₃Fe³⁺₂]Si₈O₂(OH)₂ that is unique in that both ferrous and ferric iron are present.  The mineral, with a hardness of 5-6, is usually dark blue to black in color and the crystals are columnar aggregates.  The ends of the individual columns are usually broken and rarely terminated.  My specimen is actually pegmatitic in nature. 

One interesting aspect of the riebeckite-bearing Mount Rosa Granite is the level of radioactivity present, mostly due to the presence of thorium.  Exploration pits have been constructed and 500 tons of ore were processed for their radioactive content; however, commercial processing seems unfeasible (I think) (Gross and Heinrich, 1966).

And finally, a variety of riebeckite termed crocidolite is an “asbestos” mineral with a fibrous habit and dangerous if ingested.  

REFERENCES CITED

Gross, E. B. and E. W. Heinrich, 1965, Petrology and Mineralogy of the Mount Rosa Area, El Paso and Teller Counties, Colorado: I The Granites:  The American Mineralogist, v. 50.

Gross, E. B. and E. W. Heinrich, 1966, Petrology and Mineralogy of the Mount Rosa Area, El Paso and Teller Counties, Colorado: III Lamprophyres and Mineral Deposits:  The American Mineralogist, v. 51.

Smith, D. R. and J. Noblett, R. A. Wobus, D. Unruh, K. R. Chamberlain, 1999, A review of the Pikes peak Batholith, Front Range, Central Colorado: A “Type Example” of A-type Granitic Magmatism: Rocky Mountain geology, v. 34, no. 2.

FOX HILLS FORMATION

Discoscaphites collected from Fox Hills Formation, South Dakota.

 

There are a number of quite interesting highways traversing east-west across northern South Dakota; however, my favorite is the somewhat lonely SD 20 heading east from Reva Gap to Mobridge on the Missouri River.  Actually the road starts at the Wyoming-South Dakota state line at Camp Crook.  This route crosses over a variety of rocks that are somewhat unfamiliar to readers in Colorado Springs.   Above the ubiquitous Pierre Shale are the, in ascending order, Fox Hills Formation, Hell Creek Formation, Ludlow Formation, Cannonball Formation, and Tongue River Formation.

The Fox Hills, a unit that is also present around Colorado Springs, grades upward from the marine shales of the Pierre into marine and then into marine and brackish water sandstones.  The unit represents the end of the great Western Interior Seaway and rocks are essentially shoreline deposits of the receding waters.  Although the Fox Hills near Colorado Springs contains a few fossils, mostly small clams, there are parts of the formation in north-central South Dakota that are extremely fossiliferous.  Some concretion layers have produced literally thousands, perhaps tens of thousands, of beautiful ammonites (and a plethora of other invertebrates and vertebrates), especially of the genera Discoscaphites , Sphenodiscus, and Hoploscaphites.  They represent some of the youngest ammonites in the U. S. (remember the ammonites became extinct at the end of the Cretaceous). 

Somewhere around the town of Timber Lake, a “long time ago”, I was able to collect some of these concretions with most specimens going to a museum.  However, I was able to hold on to a single specimen. Perhaps individuals may still collect on private lands.

mike

COLORADO SILVER, THE SHERMAN BROTHERS, AND MORGANITE

MINE DUMPS WEST OF CARBONATE HILL, LEADVILLE, CO.  LEADVILLE WAS ONE OF THE LARGEST SILVER CAMPS IN THE WORLD UNTIL THE 1893 CRASH.  PHOTO FROM USGS LIBRARY.

 Most persons with at least a passing interest in U.S. history would recognize the name of William Tecumseh Sherman, and if you lived in the southeastern part of the country the mention of his name in public might bring on trouble.  Likewise, Sherman is not popular among Native Americans.  During the U.S. Civil War General Sherman led his men on the infamous, scorched earth, “total war”, march to the sea through Georgia.  After the conflict he became Commanding General of the United States Army and as such was responsible for troops engaged in hostile actions with Native Americans in the western U. S.

General Sherman had a brother (actually he had three) by the name of John Sherman who was a successful U.S. Congressman, Senator, Secretary of the Treasury, and Secretary of State.  Today people hear his name associated with a law passed in 1890, The Sherman Antitrust Act.  This piece of legislation is intended to protect the American public from cartels and monopolies.

In the history of Colorado (and some other western states) Sen. John Sherman, Chair of the Senate Finance Committee, is known as the author of the Sherman Silver Purchase Act enacted in 1890.  This legislation stipulated that the U. S. government purchase about 4.5 million ounces of raw silver every month (in addition to silver already being purchased as mandated by the Bland-Allison Act).  The Sherman Act was a great boon to Colorado mining companies that had a vast supply of silver at their disposal, both in storage and in the ground, and raised the price of silver to over $1 ounce.  But since Sherman was a senator from an agrarian state (Ohio) the act was supposed to help farmers who had accumulated large debts (mostly to due to bad luck and droughts).  Supporters thought the law would stimulate the economy, combat deflation, create inflation, and then drop the dollar in value (so the debts could be paid in cheaper dollars---and I thought “voodoo economics” was invented in 1980).  Well, the entire scheme backfired and people begin to buy gold with their redeemable notes, rather than holding silver, and the country’s gold reserves became depleted.  In 1893 President Grover Cleveland repealed the Act and silver was on its way out and most mines in Colorado suffered.  Large scale unemployment was rampant in Colorado and mines all over the state closed down.  The “lucky” ones were able to produce gold or copper or lead-zinc.

Today, J. P. Morgan Chase & Co. seems always to be in the news---mostly as the “bad guy”.   In the late 1800’s and early 1900’s J. P. Morgan, the financier, always seemed to be in the news---often as the “bad guy”.  However, in 1893 the U.S. Treasury had been nearly depleted of gold as banks thought gold a better investment than silver, something the Sherman Act did not anticipate.  At any rate, J. P. Morgan, the financier, sold/loaned the U.S. about 3.5 million ounces of gold.  Always the shrew banker, he received a long term bond in exchange for the gold and certainly made money.  But, his immediate action did perhaps save the nation?  Could any individual, today, come up with those sorts of resources?

It is interesting to note that although the Act was repealed in 1893, the debate on the national scene went on for many years.  History books in “my era” (a long time ago) spent several pages talking about the “Goldbugs” of the Republicans and Wm. McKinley (a gold standard) vs. the “Silverites” of the Populists and Democrats and Wm. Jennings Brian (free silver) in the presidential election of 1896.  The free silver issue really was not settled until the Federal Reserve System was established in 1913.  But, hold on.  Many of us can remember how two brothers from Texas tried to corner the silver market in the 1970’s and early 1980’s.  In the early 1970’s the price of silver on the commodities market was less than $2 per oz.  By about 1980 the brothers owned 50% of the disposable silver and prices artificially soared to over $50 an oz.  Silver mines all over the west were retooling and share prices of silver mining companies were high (at least out of my reach as a small time investor)!  But then, the bubble burst as the Federal Reserve “came to the rescue” and the price of silver collapsed (as did the stock market; remember the prime rate of 22% in 1980?).

Perhaps the political intrigue of that time in history was just as dark and dirty as today?  I once read a bibliography of J. P. Morgan and it was simply fascinating.  He was an astute businessman involved in a wide range of activities and “older” (read my generation) history books will tell you that he organized over 40 corporations and owned numerous railroads, a true venture capitalist.  He was disliked by many but loved by a few.

Morgan collected gemstones, many/most of which later landed in collections of the American Museum of Natural History. George Kunz, the chief jeweler for Tiffany & Co, suggested in 1910/1911 that the pink variety of beryl [Be₃Al₂(SiO₃)₆] be named morganite after J. P.  Of course, Kunz was the person who curated Morgan’s gemstones.  Kunz may be best known for  his namesake, the pink variety of spodumene, kunzite [LiAl(SiO₃)₂].  The pink color in both morganite and kunzite is likely due to manganese ions.

mike

BLM RAC: LOOKING FOR A FEW GOOD MEN AND WOMEN

The Bureau of Land Management (BLM) is the guardian of a very large parcel of public land in the state of Colorado- perhaps in excess of 8.4 million surface acres and controlling 29 million acres of subsurface mineral rights.  The BLM has a state office in Denver and Helen Hankins is the State Director (www.blm.gov/co/st/en.html).  The state is then divided into three districts:  Front Range District with headquarters in Canon City, the Northwest District headquartered in Grand Junction, and the Southwest District with offices in Montrose.  In addition, each of the District Managers is responsible for several field offices (that also have Managers).  For example, the Front Range District Office (FRDO) manages most BLM lands in Colorado east of the Continental Divide and has field offices located in Canon City (Royal Gorge), Saguache (San Luis Valley) and Salida (Arkansas Headwaters Recreation Area).  Each of the three state Districts have a citizen’s advisory committee (~12 members) that meets quarterly (as do most districts located in the western states).  I serve on the Front Range Resource Advisory Committee (RAC) and would encourage other interested rock hounds to consider service on these important councils.  We recently have studied such diverse items as feral horse populations, the Over the River Project©, geothermal leases, shooting ranges, and gold mining.  Since I represent the “dispersed recreation community” (things like rock hounding and recreational gold panning), I am always interested in any legislation or rule changes concerning collecting of rocks, minerals and fossils, and proposed changes to land access.

The Front Range Resource Advisory Committee is seeking nominations (self nominations are fine) for five new members (including dispersed recreation activities).  The deadline for receipt of nominations has been extended to June 4.  For information see:  http://www.blm.gov/co/st/en/BLM_Information/newsroom/2012/blm_extends_nomination0.html

UTAH AMETHYST AND GEORGE CLOONEY

BIG ROCK CANDY MOUNTAIN, MARYSVALE, UTAH.  PHOTO COURTESY OF RAY BOREN AND NASA'S EARTH SCIENCE DIVISION

One of my favorite movies is a loopy flick entitled Brother Where Art Thou directed by those talented brothers, Joel and Ethan Coen, in 2000—a great film for an interesting year, Y2K.  The movie had many memorable scenes and some fantastic music including the song Big Rock Candy Mountain:

Oh the buzzin’ of bees in the cigarette trees

and the soda water fountain,

at the lemonade springs where the bluebird sings

on the Big Rock Candy Mountain.  

 

Check out the music clip at: http://www.youtube.com/watch?v=KSGuBNopzBw&feature=player_embedded

Hearing the song always reminds me of a student field trip in Utah to a pile of volcanic rocks near the town of Marysvale. The most “famous landmark” of these volcanics is, get ready, Big Rock Candy Mountain.  So, in the "which came first game", I was able to learn that the song is some sort of a depression-era folk tune attributed to Harry McClintock (~1928) and recorded by several other artists including Burl Ives and Tex Ritter.  Our instructor told us that members of the local population placed a hand-made sign near the mountain proclaiming it as Big Rock Candy Mountain and the name stuck.  Today it is a tourist attraction—and an area of interesting geology. 

The area around Marysvale (Piute County, south-central Utah) is dominated by Oligocene to early Miocene volcanic rocks (27 Ma to 19 Ma) associated with a large stratovolcano complex complete with calderas (Hintze, 2005) ---similar in many ways to the current Cascade volcanoes of Washington and Oregon.  The volcanic pile is composed of drab-gray debris flows, lava flows, ash fall tuffs, and pyroclastic flows (ignimbrites).  The brightly colored volcanic rocks at Big Rock Candy Mountain are the result of percolating hot magmatic waters bleaching the normally dark volcanic rocks and leaving behind red, orange and yellow iron oxide stains (Hintze, 2005).

Topaz-bearing volcanic rhyolites (extrusive igneous rocks, rich in silica) in Utah are perhaps best known from the Thomas Range in the western part of the state.  These rhyolites have produced the famous topaz crystals of Topaz Cove, and some other interesting minerals (see blog post on 1 March 12)

Similar rhyolite flows are present in the Marysvale area and have produced some of the same semi-rare minerals such as bixbyite and pseudobrookite, but not the nice topaz crystals.  To make up for the absence of large topaz crystals the rhyolite at Marysvale gives up beautiful, terminated, water-clear, purple-tinged, quartz crystals.  The crystals are lithophysal in nature and collectors must bang on the rhyolite with crack hammers to locate the cavities.  The collecting area is on BLM land (I think but make certain you check with the local office) about 3 miles north of town on US 89 and then west on a gravel road.

mike

PURPLE TINGED QUARTZ CRYSTALS (AMETHYST) IN A RHYOLITE CAVITY; AT MARYSVALE, UTAH.  FIELD OF VIEW ~3 CM. WIDE.

REFERENCES CITED

Hintze, L. F., 2005, Utah's Spectacular geology; How It Came To Be: Department of Geology, Brigham Young University, Provo.

FROM THE FILM

(Nothing to do with amethyst but my favorite quote; warped mind?)
MOVIE SCENE

Delmer, Pete and Everett sitting around a campfire "enjoying" dinner.

  

DELMAR: Care for some gopher? 
EVERETT (George Clooney): No thank you, Delmar. One third of a gopher would only arouse my appetite without bedding it down.
DELMER; Oh, you can have the whole thing. Me and Pete already had one apiece. We ran across a whole... gopher village. 

POST SCRIPT

So the question in my mind, and probably only in mine, is just exactly what were Delmer and Pete really eating down there in rural Mississippi in 1937?  Gopher--that much we know.  But "gopher" is sort of a generic term like "Coke" referring to just about any soft drink.  In the Midwest "gopher snakes" refer to Bull Snakes (Pituophis catenifer).  Gopher Tortoises (Gopherus polyphemus) are "land turtle" found in the southeastern U.S.  But, most people think of a "gopher" as some little furry creature that burrows into the ground.  And, in fact, there is a family of rodents known as the Geomyidae that are the Pocket Gophers.  In the movie, it was obvious the little animal roasting over the fire on the skewer was a small mammal, about the size of a Pocket Gopher, so count out the tortoises and snakes.  And, unfortunately, the Pocket Gophers since their range does not include Mississippi!  The roasting dinner was too small for a Woodchuck (Marmota monax) and too big for any of the "mouse" species found in the state.  The Eastern Woodrats (Neotoma floridans) might fit the size bill; however, I have never heard these animals called "gophers".  That leaves the Eastern Chipmunk (Tamias striatus), a furry little burrowing rodent, as the best suspect; but, it seems somewhat small compared to the roasting animal!  And, have you ever tried to catch a chipmunk?  Oh well, life goes on.

A MINNESOTA GOLDEN GOPHER---THE "REAL THING", AND FANS OF THE UNIVERSITY OF MINNESOTA BASKETBALL TEAM.  PHOTO COURTESY OF U OF M.

FROM THE FILM