Calcite Vug at Bear Lake
Research Area, Alaska
Dr. Michelle M. McGee

Preface Introduction Chemistry & Science Colors Accessory Minerals Uses Forms Crystals Limestone Geology Travertine Tufa Banded Calcite Alabaster Caves Speleothems Visiting Underground Caves: What's Inside? Cave Links Vugs Alaskan Vugs Local Vugs Lapidary Famous Locales Cave Lore Endnotes Article Contributors Photo & Graphics Credits Suggested Reading Webliography Invitation to Members Past Minerals of the Month		Manganoan Calcite on Quartz Pachapaqui Mine, Ancash, Peru	Calcite Crystal Hanson Quarry, North Vernon, IN
		Calcite is both common and extraordinary at the same time...
		Sapphire on Calcite Mogok, Burma	Calcite with Hematite Inclusions Egremont, Cumbria, England
		...so, travel with me to witness these wonders for yourself!
		The above images are courtesy of Isaias Casanova of IC Minerals ©2005

Preface

     Our March Mineral-of-the-Month is Calcite.  It has more forms than most other minerals;
and, that is what we will concern ourselves with in this article.  We will touch lightly upon its
science and chemistry, but will mainly focus on the variety of magnificent forms its takes in
nature.  This article is by no means comprehensive on the subject, as many volumes would be
needed—possibly a lifetime’s work could be devoted to this favored mineral.  So, we will embark
upon an odyssey of form and function, to places wherein the calcite can surround us in often
voluminous, echoing spaces.  Also, we shall visit locales that I hope will enjoin you to visit, and in
some, collect your own specimens of this awesome wonder.  

     As you might expect, our journey today takes us not only into the basic science of Calcite,
but into its surface, underwater, and underground homes.  We will visit pinnacles, caves and vugs,
as well as exotic and common crystal forms around the United States and parts of the world.  
Among these places are ancient caves around the U. S. and Spain, curious vugs in Alaska, and
a virtual tour of enticing crystals from around the world.

Inside Carlsbad Caverns, New Mexico

     For some calcite enthusiasts, crystals are the key to their excitement about our hobby.  To
others, visiting the naturally air-conditioned, underground sites suits their fancy. Purveyors of fine
specimens might agree that no matter what the source, calcite has a lure all its own. 

Crystals...		Caves...		and Vugs
Calcite, Sweetwater Mine, Reynolds County, MO		Bear Creek Research Area, AK		Calcite from Franklin, NJ
Courtesy of: Isaias Casanova		Dr. Michelle M. McGee		Ken Casey

     From a quick viewing of photos on this page, we can witness outstanding rhombs and prisms,
free-form speleothems, and encrusted vessels of this crystallized carbonate, famously called vugs. 
Our journey continues with a larger than life experience, as we might imagine our curiosity pulling
us into the cheery, ‘mega-vugged’ tunnels of near darkness, wondering what odd form we may find
around the corner on our caving tours.     

     Before any spelunking, however, it is helpful to have a basic understanding of calcite’s chemistry,
forms, and habits to appreciate the wonders we will see below.  As always, remember to put on
your hard hat!

     Calcite is calcium carbonate (CaCO₃).  The name ‘calcite’ derives from the Greek word for lime,
"chalix".[i]   The etymology progresses from Greek to Latin, then to “Middle English, from Old English cealk, from Latin calx, calc-, lime; see calx” [ii]   Today, you may see a package of lime labeled: calc, calce, kalk, chaux, wapno, or bap.

Colored Chalk ©2005 Crayola, Easton, PA		Cal Agricola (Agricultural Lime) Caleras de San Cucao, S. A., Asturias, Spain

    
     Calcite crystals, caves, vugs all have their own geology.  Still, all remain chemically the same,
except for the occasional atomic addition of cations that can share or replace the calcium involved. 
These natural substitutions, included by the environment in which they formed, can affect the outward
appearance of this mineral.  For example, the presence of Manganese (Mn) can offer a pinkish cast,
hence it is named a variety of calcite, called manganocalcite (Ca, Mn)CO₃.  There are other varieties,
but we will stick with just a few here.

		2067. Calcite Var. Manganoan  Nikolayevskiy Mine, Dalnegorsk, Russia (10.5x7x6 cm) Courtesy of IC Minerals

     To touch upon its crystallography, calcite belongs to: “Crystal system: hexagonal. Cleavage:
three-directional in rhombohedron-shaped fragments. Color: usually white, but may be tinted various
colors by impurities. Hardness: 3.0. Luster: glassy. Specific gravity: 2.71.”[iii]

     Calcite can form twins and trillings, whereas aragonite can form pseudomorphs (false forms)
after other minerals, such as glauberite crystals[iv], agate fillings[v], and aragonite fans in fossil
stromatolites[vi].  Polymorphs include: vaterite.  Flosferri is the free-form of aragonite.

Mostly, aragonite decorates cave interiors, such as these stalactites in Lost River Caverns, Hellertown, PA.
Images courtesy of Mr. Gilman, Lost River Caverns

     Calcite cleaves and crystallizes in rhombs of differing measures.  The CaCO₃ of calcite and
aragonite differ by noting that the “radius ratio of Ca:O (=0.707) in CaCO₃ is so close to the limiting
value between 6 and 8 coordination (0.732) than CaCO₃ can occur in two structure types: calcite with
6 coordination of Ca to O and aragonite with 9 coordination of Ca to O.” (Dana, p. 297)[vii]

     Like fluorite, “[m]ost calcites tend to be relatively close to pure CaCO₃ with CaO 56.0 and CO2
44.0%.  Mn²⁺, Fe²⁺ and Mg may substitute for Ca and a complete solid solution series extend to
rhodochrosite, MnCO₃” (Dana, p. 298)[viii]

     For more on Calcite’s crystal morphology and science, visit Amethyst Galleries: The Mineral Calcite
and Mindat.org’s “Calcite” page.

Hexagonal-Scalenohedral Calcite Crystal		Orthorhomic-Dipyramidal Aragonite		Calcite Rhomb
(Drawings by Ken Casey © 2005)

Colors

     Depending on its paragenesis, calcite can take up almost any color from elements present at
its origin.  Colors range from red, orange, yellow, green, blue, white, gray, and colorless.  Sometimes
it occurs as multi-colored.  Chemically, it starts as basic “[c]alcium carbonate, commonly with some
impurities of either iron, magnesium, manganese, and occasionally with zinc and cobalt. Although all
impurities do not exist together, they are all listed together in the "Variable Formula" field [of the
minerals.net website] to avoid confusion. (See the Brownspar Group for more information.)”[ix]

Photo by Stan Celestian © 2005 Glendale Community College, Glenale, Arizona Specimens provided by the Arizona Mining and Mineral Museum, Susan Celestian, Curator

Accessory Minerals

     Calcite is a rock-forming mineral, and can be found in sedimentary limestone, metamorphic marble,
and chalk deposits.  There are siliceous calcites in South Dakota, and calcite is an igneous constituent
in carbonatites and nepheline syenites.  Other occurrences include crystals in lava cavities and in hydrothermal veins associated with sulfide ores.[x] (Dana, pp. 299-300)

     Calcite is so common on all continents, that even rare igneous carbonatites containing calcite have
been found in the Transantarctic Mountains of southern Antarctica.[xi]  And we have yet to scratch the
surface, which has only 2% rock outcroppings visible out from the glacial ice.

     Pyrite, chalcopyrite, fluorite, dolomite form massively, or as crystals, within our area’s limestone
quarries.  Calcite also occurs with apatite, barite, gypsum, dolomite, quartz, and wollastonite (formed
from CaCO₃ + SiO₂ à CaSi₃ + CO₂).  In Sussex County, New Jersey, it occurs with 358 zinc ore
related minerals, most notably, franklinite, willemite, and zincite, in the calcite-like Franklin Marble.[xii]

Gray Tremolite crystals in Franklin Marble		Salmon Calcite, Franklin, NJ (It fluoresces!)		White Calcite, Red Willemite, and Black Franklinite
Photos by Ken Casey © 2005

Uses

     It seems that calcite can be used in most any product, from building construction to teaching
supplies to foodstuffs.  The obvious building material is concrete, cement block, and natural
dimension stone, such as limestone, marble, and travertine.  In the classroom, we witness calcium
carbonate as paper surface-hardeners upon which our ballpoint pen writes cleanly, and as a hand-held,
narrow cylinder used for writing, also known as ‘chalk’.  Dietary supplements include antacids and
chewing gum covering.

Travertine tiles

     It also has these “[u]ses: in the form of limestone, as aggregate for road surfacing and concrete,
agricultural lime, flux, building stone, sulfur sorbents, and in cement; in the form of Iceland spar in
optical instruments to obtain polarized light.”[xiii]  Even iron-ore smelting requires some.

     Who would guess that we employ calcite in animal feed, to strengthen dough, in baking powder,
in glass making, or in photography and waste treatment plants.[xiv]

     We use calcite to build upon a grand scale.  For millennia, limestone and marble have been the building
stone of choice for much of the world's great architecture.  From the Egyptian pyramids and Greco-Roman temples of the past to today's modern government and office buildings.  Many of the federal buildings in Washington, D. C. are either built with or are faced with limestone.  The U. S. Capitol is one of these.  In the 1950s, though, the building received a much-needed upgrade from limestone to marble.  This façade should last at least another 100 years. 

U. S. Capitol Building, Washington, D. C.		Capitol Dome (marble)
Images courtesy of The Architect of the Capitol, Washington, D. C.

     We depend on this multipurpose compound for use in everyday products; and for some, for their
livelihoods.  Our club has had the good fortune to visit many rock quarries on our fieldtrips to see the
active quarrying and mining processes, as well as to collect various types of calcite.

Forms

     Crystals form into calcite, aragonite, Iceland spar, and into microcrystalline travertine, tufa and chalk. 
It metamorphoses into limestone and marble.  Varying cave forms are common, and pseudomorphs
and polymorphs abound.

Crystals

     For those who admire faceted crystals, calcite can demonstrate many forms, the most common
being prisms, rhombs, scalenohedrons, trillings, and twins.  This author has not yet studied whether
there is a direct, consistent link of color to crystal form, though believes it is worthy of further
investigation. 

     We most see calcium carbonate crystals as white, colorless, yellow, tan, gray, and salmon
colored in our region.  The first three colorations predominate eastern Pennsylvania limestones,
whereas, the second three are likely found in northern New Jersey.  The latter tend to fluoresce
under ultraviolet lamps.

Salmon calcite, Franklin, New Jersey		Salmon Calcite rhomb		White Calcite rhomb (Franklin Marble)
Photos by Ken Casey ©2005

     Our club’s fieldtrips have rewarded us with magnificent crystals of up to one-inch in length. 
Some of the best are colorless, singly-terminated scalenohedral variations.  Here are examples
from the Kurtz Quarry in Denver, Pennsylvania. 

White Calcite, Milky Quartz vein in Kurtz Limestone		Clear and Milky Calcite, Pink Dolomite, and Purple Fluorite vug, Kurtz Quarry
Photos by Ken Casey ©2005

     Beyond our club’s general collecting range lies numerous locales that popularize this laudable
mineral.  One of our March Show vendors, Isaias Casanova of IC Minerals, has generously lent
some of his calcite collection photos for us to wow over.

IC Minerals Calcite Slideshows: Calcite slide show (Internet Explorer) Calcite slide show (Netscape) [Best viewed in "Full Screen" or "F11"] Image of Calcite from IC Minerals

Limestone Geology

     Karstic activity spawns travertine and tufa as groundwater is forced through limestone as part of
earth’s carbon cycle. “In many locations with karst, CO₂ emission is associated with the deposition
of calcareous sinter (e.g., tufa and travertine) at the outlet of cold or warm springs (Berger 1995).”[xv]

     It is amazing that “[a] fifth of the landscapes in the United States are karstic. Major karst areas
occur in 20 states, and smaller karst regions occur throughout the nation. Many major cities are
underlain in part by karst, such as Saint Louis, Missouri; Nashville, Tennessee; Birmingham,
Alabama; and Austin, Texas.”[xvi]

Karst Topography		Calcite Jungle at Cave of the Winds, South Dakota		Cave-divers at John Eddings Cave NPS Photo by Carol Bitting
Courtesy of the National Park Service (NPS Photos)

     Undersea caves also exist to visit by engaging in the extreme sport of cave diving.  These exist
as most limestone is of marine deposition.  Orogenies (mountain-building events) have pushed ancient
layers to the surface. 

     Erosion and groundwater take their toll, thus forming the terrestrial tunnels that we shall explore
here. Thusly, the possibility of continent-wide cave formation, travertine and tufa deposition, and
metamorphic calcite crystal vugs leaves us many locales to explore.  Let's go!

     I will begin by introducing some above ground calcite formations.

Travertine

     Travertine forms from underground magma that geothermally heats mineral-laden water springs. 
The resultant rising steam pressure forces the superheated water to the surface, where it evaporates,
leaving behind thin layers of accumulating travertine.   A good example is Mammoth Hot Springs in
Yellowstone National Park.  The park covers the borders of three states: Idaho, Montana, and
Wyoming.

Picture of hot springs and resultant travertine, Yellowstone National Park (NPS Photo)

     A cool site to visit is the Old Faithful Geyser webcam.  It’s the next best thing to watching the
travertine form in person.

Tufa 

     Tufa is formed as cold water dissolves surrounding calcareous rocks.  As the water flows, it leaves
calcite to deposit as microcrystals.  Iron oxides may accompany the calcium carbonate, thus
resulting in red and yellow staining of the newly formed layers.  Sometimes, plants and animals can
become trapped and coated to later form fossils.[xvii]

     The Rocky Mountain region contains various tufa topographies.   Some tufa (pronounced “toofa”)
examples are found in the Trona Pinnacles National Natural Landmark near Argus, California. 
Utah’s Lake Bonneville shoreline consists of Pleistocene sedimentary tufa, whereas the tufa towers
of Mono Lake, California have formed of spring water mixing with lake water.[xviii]

     The chemical reaction precipitates into slow growing towers.[xix]  The bases begin near or under
the lake waters, and build from there upwards.

Tufa deposits at Trona Pinnacle National Landmark, California (NPS Photo)

Banded Calcite

     Banded Calcite resembles onyx, however, it is actually calcium carbonate.  It goes by locality
names, such as Mexican onyx from Baja and Mt. Nebo Onyx from Utah.  ”The Mt. Nebo deposit
consists of reddish-orange and cream-colored banded calcite. Calcite is composed of calcium
carbonate (CaCO₃). Banded calcite is formed when calcium carbonate precipitates (separates out)
from a solution of dissolved calcium carbonate and ground water. The calcium carbonate is deposited
within a large opening or fissure in the mother rock and parallel bands are created as additional
calcium carbonate precipitates.

Mt. Nebo Onyx		Guatamala-Maya Calcite alabaster vase
Photo by Ken Casey © 2002-2005		U. S. Department of State

     “The changes in the color banding are probably caused by slight changes in the chemical
composition of ground water during precipitation. The Mt. Nebo banded calcite can be polished and
used for decorative purposes, such as bookends.”[xx]

Alabaster

     Alabaster is known as a form of gypsum.  It also refers to a similar looking rock form of calcite,
and is used for the same purposes: decorative carving.  (See 'alabaster vase' photo above.)

Caves

     We will now go underground, traversing through the cave mouth, and climbing downward on a
mild slope, until we reach our first of nature’s decorations.  Watch your step!

     Aragonite forms crystals in vugs and stalactites/stalagmites (varieties of speleothems), and in
caves as calcite or aragonite.  It may contain strontium, lead, or zinc, as well. 

     “Cave formations are called speleothem, from the Greek word "spelaion", cave and "thema"
meaning deposit.  Almost all of them are made of calcite, the crystal of calcium carbonate.
Different minerals and different movements in the water account for an incredible variety of cave
formations.”[xxi]

Aragonite speleothem pictures: cave bacon, flosferri, and stalactite/stalagmites
Various National Park Service Caves (NPS Photo)

Speleothems

     “Speleothems are cave formations. Specifically, the term is applied only to deposits formed
from a chemical solution or by the solidification of a fluid after the formation of a cave. Stalactites
are speleothems, as are ice crystals formed directly form water vapor in a cave; but beds of silt,
and calcite veins etched into relief when the walls of the cave dissolved, are not.   Source: Moore
and Sullivan (1997)”[xxii]

     These form in “solution caves”, in which acidic groundwater travels through earth’s stress
cracks and dissolves limestone.  The flow then drips down from cave ceilings to create stalactites. 
The falling water then hits the cave floor, hence building up stalagmites.  One mnemonic device to
remember which is which, is to use a differing letter in the third syllable of each term.  Use “T” for
stalactite (it looks like it is pointing down, and “M” for stalagmite (the humps on the “M” appear to
be pointing up).

     Incrustations can form as the mineral-laden ground water drips and runs over the cave
topography.  These form curving, translucent shapes resembling strips of bacon, animals, and
pipe organs, to name a few.   Sometimes these curious forms are obvious; often, they require
one’s imagination.  Cave tourism is built upon our curiousity to witness these imaginative sites.

Aragonite Tree				Stalactites & Stalagmites
Soda Straw (above) Fried Egg Stalagmite (below)				(NPS Photo)

Visiting Underground

     There are many such caves open to the public for a fee to tour in our club’s area.  Two
examples are: Lost River Caverns in Hellertown, Pennsylvania and Crystal Cave Park in Kutztown. 
Only one known real cave exists in our state.  It is the Beaver Valley Cave in New Castle County,
Delaware.  However, advanced caving skills are required, and the only current access is through
the Commander Cody Caving Club.  I visited the Lost River Caverns about three years ago, and the
tour was most fascinating.  It is a good day trip for families, groups, or individuals.

     America’s topography is riddled with caves found in most states.   There are too many to list
here, so I will suggest a few outstanding examples, along with those administered by our
National Parks Service.  You will find the list below.

     Some people live in caves.  Both ancient and modern man share this distinction as ‘cave-dweller’. 
The historic cave paintings of Lascaux Cave in France support this hypothesis.  Other caves around
the world have also left evidence for us to ascertain this fact.  Neanderthal man has called them his
home in Europe and the Middle East.

     Today, some still enjoy their ‘digs’ underground.   In Spain’s Andalusia region a whole community
is situated in them.  The Cuevas Galera Complex touts modern conveniences, as well.   There are
comfortable abodes nestled in the mountains and plains of the United States.  For example, two such
established living quarters comprise the bulk of a cave entrance in Parthenon, Arkansas, and one in Armington, Illinois.

     More information may be found on the Home & Garden Television website.  Just search for the
show “Extreme Homes” episodes: EXT-314, SUB-S or search for (“cave” AND “home”) for a listing. 
There is even a bed-and-breakfast at Kokopelli’s Cave in Farmington, New Mexico.  Just reference
“Dream Builders” episode DRB-801 at www.hgtv.com.

     Some 19th & 20th century American outlaws would hideout in caves.  Treasure hunters have
recently uncovered relics of the fugitives who stayed in one Oklahoma cave.  The Knights of the
Golden Circle and Outlaw Treasure website offers us a view of famous cave-dwelling lawbreakers.

Caves: What’s Inside

     While wondering into a cool, dank cave ecosystem, you may find the inhabitants (troglobites). 
You might feel silent air currents, signaling a larger cave beyond.  The average annual surface
temperature will be how cool your skin will feel while exploring.  Many U. S. caves hover around
55 degrees Fahrenheit.  So dress warmly on your visits.

     You may forget your initial reaction to your new environs, as you extend your experience into the
visual—the lighted passageways beckoning you, along with your tour guide calling you to move inside toward these fantastic natural wonders.  For the spelunker (cave explorer), you must bring your own illumination and gear.   You may wish to explore  these caves below.  Let's go in!

Entrance to Carlsbad Caverns, New Mexico		Lanterns to light our way		NPS Ranger giving Cave tour
Courtesy of National Park Service Photos

Cave Links

Vugs

     “What is a vug? Vug is derived from a Cornish term, 'vuggh', meaning crystal-lined cavity. The
mines of Cornwall, England, have produced metal ores and mineral specimens since the 5th century,
so many mining terms are of Cornish origin.”[xxiv]

     The vugs we will be exploring contain phenomenal calcite crystals.  These small caves can
house well-preserved crystals for eons, mainly because vugs are usually sealed off from the outside
air and weather.  Usually, it is the fortunate rockhound who breaks open a likely candidate boulder to
expose beautifully faceted calcite crystals.  Our club has visited two limestone quarries this past year
to find varieties of clear, white, and yellowish terminated crystals.

     The limestone of both the Kurtz and Binkley-Ober quarries is hard to work, but worth the effort. 
The products of our hosts are aggregate and concrete block, respectively.  Having a working knowledge
of local geology can assist both the experienced and novice field collector.  The purpose for the quarry’s
output can be a guide the relative hardness of the local stone.  Also, by ascertaining the general
porosity of the host rock (matrix), one can project the possibility of vugs to increase his or her chances
of opening ones with calcite crystals.

     This sample research, conducted by the Laboratory for Computational Geodynamics at Indiana
University, shows the approach to advanced geology and materials science.  It is your choice as to
how much you would like to learn to enhance your rockhounding experience.

     “Calcite-dolomite host rock with porosity of 0.20. The stresses are normal overburden stresses
and fluid pressure is hydrostatic with water table at the surface of the basin. Horizontal stresses are
computed by constraining the lateral displacement. Highly asymmetric vugs survive below 3000
meters when oriented vertically, but the ones oriented vertically fail after 1100 meters.”[xxv]

Chart of porosity test for Calcite/Dolomite
Laboratory for Computational Geodynamics, Indiana University

Alaskan Vugs

     Dr. Michelle McGee, graduate of the University of Alaska, has conducted field research in
the limestones of northern Alaska.  The Bear Creek Field Area plays home to many small caves
and calcite-lined vugs.  The crystals formed around other fossilized marine organisms, such as
coral.

    “These photos are of the Carboniferous lower Lisburne Group in the Arctic National Wildlife
Refuge (Northeastern Brooks Range), Alaska." --Dr. McGee

This vug occurs in the middle of a large Syringaporid coral.