Mark Taylor / Calcium carbonate covered plants in hot spring, Yellowstone National Park, Wyoming, USA

Mark Taylor / Calcium carbonate covered plants in hot spring, Yellowstone National Park, Wyoming, USA

Jack Dykinga / Dawn at Inspiration Point, with calcium carbonate hoodoo formations glowing, Bryce Canyon National Park, Utah, USA

Jack Dykinga / Calcium carbinate hoodoos with reflected light of dawn above the conifer lined valley below, Bryce Canyon National Park, Utah, USA

Erlend Haarberg / Curved layers of marble and calcium-silicate flowing around mica schist from the Engabreen Glacier, Saltfjellet-Svartisen National Park, Nordland, Norway, September 2006

David Maitland / Cross section through Spine of Sea Urchin (Echinus lividus) shows how its entire structure is made up from a repeating “building-block” pattern of calcium carbonate plates arranged radially in a symme...

Diane McAllister / Northwestern fence lizard / Blue bellied lizard (Sceloporus occidentalis occidentalis) sunning itself on a fencepost. It is molting and will consume the shed skin for calcium and other nutrients. Palo...

Nick Upton / Grasses, mosses and Butterbur (Petasites) growing around waterfall as curtains of calcium laden water tumble down, forming travertine limestone at Plitvice Lakes National Park, Croatia, July 2010.

Nick Upton / Close up of porous travertine limestone formed in a waterfall by calcium laden water tumbling over rocks covered with moss and other vegetation at Krka National Park, Croatia, July 2010.

Nick Upton / Sycamore (Acer pseudoplatanus) and other trees overhang waterfalls with travertine limestone forming as calcium laden water tumbles down moss covered rocks at Plitvice Lakes National Park, Croatia, Ju...

John Cancalosi / Fluorite (CaF2) (calcium fluoride) on Sphalerite (ZnS) (zinc sulfide) Elmwood Mine - Smith County - Tennessee - USA - Fluorite is a source of fluorine-used in the manufacture of milk glass-as a flux...

John Cancalosi / Selenite (CaSO4-2H2O) (Hydrous calcium sulfate) Form of Gypsum, from Australia. Formed in evaporite deposits. Green colour caused by leaching from mine waste

John Cancalosi / Fluorite (CaF2-calcium fluoride) and Galena (PbS - lead sulfide) and Quartz (SiO2 - silicon dioxide) - Blanchard Mine - Portales Tunnel - Socorro County - New Mexico -Fluorite (purple) is one of the m...

Steven David Miller / Ngilgi Cave is in a system of limestone caves richly decorated with the calcium carbonate formations including this stalactite tipped with a cluster of crystals. The clear straw at the base is man-ma...

Steven David Miller / Ngilgi Cave is in a system of limestone caves richly decorated with the calcium carbonate formations including flowstone. Leeuwin-Naturaliste National Park, Southwest Western Australia

Steven David Miller / Ngilgi Cave is in a system of limestone caves richly decorated with the calcium carbonate formations including flowstone. Leeuwin-Naturaliste National Park, Southwest Western Australia

Steven David Miller / Ngilgi Cave is in a system of limestone caves richly decorated with the calcium carbonate formations including flowstone. Leeuwin-Naturaliste National Park, Southwest Western Australia

Steven David Miller / Ngilgi Cave, a limestone cave richly decorated with the calcium carbonate formations including flowstone resembling shawls or slabs of bacon. Leeuwin-Naturaliste National Park, Southwest Western Aus...

Thomas Lazar / Morning light on calcium carbonate Tufa towers in mineral rice lake waters, Mono Basin National Forest Scenic Area, INYO National Forest, California, USA, June 2008

Philippe Clement / Tubes of of calcium carbonate from a serpulid worm attached to shell on beach, Brittany, France

Philippe Clement / Tubes of of calcium carbonate from a serpulid worm attached to mollusc shell, Brittany, France

Juergen Freund / Shell / test of a Foraminifer (or "Foram"), an important source of calcium carbonate in marine sediments and sedimentary rocks

Juergen Freund / Blocks of soft coquina limestone formed from shells of Bivalve Cardiid Cockle {Fragrum erugatum} Rainwater repeatedly dissolves small quantities of calcium carbonate of which the shells are composed....

Jason Smalley / The White Desert, near Bahariya, Egypt, with unusual rock formations caused by wind eroding the calcium rich rock.

Jason Smalley / The White Desert, near Bahariya, Egypt. The unusual sculptures are eroded by the wind from the calcium rich rock.

Jason Smalley / The White Desert, near Bahariya, Egypt, with unusual rock formations caused by wind eroding the calcium rich rock.

Jason Smalley / The White Desert, Western Desert, Egypt, with rock formations caused by wind erosion.

Jason Smalley / The White Desert, near Bahariya, Egypt, with unusual round rock formations caused by wind eroding the calcium rich rock.

Jason Smalley / The White Desert, near Bahariya, Egypt, with unusual rock formations caused by wind eroding the calcium rich rock.

Jason Smalley / The White Desert, near Bahariya, Egypt, with unusual rock formations caused by wind eroding the calcium rich rock.

Adrian Davies / Tufa towers, Mono Lake, California, USA

Adrian Davies / Tufa towers, Mono Lake, California, USA

Adrian Davies / Tufa towers, Mono Lake, California, USA

Staffan Widstrand / Year-old Grey wolf droppings, white from calcium content, Varmland, Sweden.

Dave Watts / Reticulated giraffe {Giraffa camelopardalis reticulata} chewing bone for calcium, South Africa Ithala

John Cancalosi / Calcium carbonate rock Sahara desert Morocco

Phil Savoie / Gypsum crystals (Calcium sulphate) cover the ground White sands NM, New Mexico, USA

Phil Savoie / Gypsum crystals (Calcium sulphate) cover the ground White sands NM, New Mexico, USA

Constantinos Petrinos / Bleached soft leather coral {Sinularia sp} Sulawesi Indonesia. Temperature change results in loss of symbiotic zooxanthellae from tissues of polyps, this exposes white calcium carbonate skeleton.

Doug Wechsler / Tufa towers of calcium carbonate formed by alkaline spring water. Mono Lake, California, USA

Paul D Stewart / Chromolithograph illustration of Cromagnon 'Skull of an old man' Plate 1, Section C. Edouard Lartet and Henry Christy. 'Reliquiae Aquitanicae' 1865-1875, Williams and Norgate, London 1875. The type sp...

John Cancalosi / Fluorite (CaF2, calcium fluoride) on Sphalerite (ZnS, zinc sulfide). Fluorite is a source of fluorine-used in the manufacture of milk glass-as a flux for the steel industry and in refining of aluminum...

John Cancalosi / Fluorite with Calcite, (CaF2-calcium fluoride). Fluorite is one of the most popular minerals among collectors, Mineral class: Halides. Fluorite is a source of fluorine-used in the manufacture of milk...

John Cancalosi / Fluorite with Calcite, (CaF2-calcium fluoride). Fluorite is one of the most popular minerals among collectors, Mineral class: Halides. Fluorite is a source of fluorine-used in the manufacture of milk...

John Cancalosi / Selenite (CaSO4-2H2O) (Hydrous calcium sulfate), a form of gypsum. Sample from Mt. Gunson, Australia. Formed in evaporite deposits.

John Cancalosi / Fluorite (CaF2) (calcium fluoride) on Sphalerite (ZnS) (zinc sulfide).Fluorite is a source of fluorine-used in the manufacture of milk glass-as a flux for the steel industry and in refining of aluminu...

John Cancalosi / Calcite (Ca CO3, calcium carbonate), one of the most common and variable minerals on earth, used in building, metallugy, fertilizers, chemical industry, with pyrite and marcasite. Sample from Conco Mi...

John Cancalosi / Calcite, (CaCO3, calcium carbonate), one of the most common and variable minerals on earth, used in building, metallugy, fertilizers, chemical industry. Sample from Sweetwater mine, Viburnum trend, Mi...

John Cancalosi / Calcite (Ca CO3, calcium carbonate), one of the most common and variable minerals on earth, used in building, metallugy, fertilizers, chemical industry, with pyrite and marcasite. Sample from Conco Mi...

John Cancalosi / Calcite, (CaCO3, calcium carbonate), one of the most common and variable minerals on earth, used in building, metallugy, fertilizers, chemical industry, also with some chalcopyrite (iridescent). Sampl...

John Cancalosi / Calcite (Ca CO3, calcium carbonate), one of the most common and variable minerals on earth, used in building, metallugy, fertilizers, chemical industry, with pyrite and marcasite. Sample from Conco Mi...

John Cancalosi / Selenite (CaSO4-2H2O, Hydrous calcium sulfate), a form of Gypsum formed in evaporite deposits. Mexico

John Cancalosi / Fluorite (CaF2, calcium fluoride), a halide mineral and one of the most popular among collectors. Used as a source of fluorine, in the manufacture of milk glass, as a flux for the steel industry and i...

John Cancalosi / Fluorite (CaF2, calcium fluoride), a halide mineral and one of the most popular among collectors. Used as a source of fluorine, in the manufacture of milk glass, as a flux for the steel industry and i...

John Cancalosi / Scheelite (CaWO4, Calcium tungstate), an ore of tungsten. It is flourescent and deposits are often found by prospecting with UV lights. China

John Cancalosi / Fluorite (CaF2, Calcium fluoride) and Galena (PbS, Lead sulphide). Rogerley Mine, County Durham, England, UK

John Cancalosi / Selenite (CaSO4-2H2O, Hydrous Calcium sulfate), a crystalline form of gypsum. The massive form of gypsum, found in alabaster, is widespread and commercially important, used for the manufacture of plas...

John Cancalosi / Calcite crystal (CaCO3, calcium carbonate) covered with siderite (FeCO3, iron carbonate). Drouba Mine, Rhodopi Mountains, Bulgaria

John Cancalosi / Purple Fluorite (CaF2, calcium fluoride) fluorite, a halide mineral. Fluorite is one of the most popular minerals among collectors. Used as a source of fluorine, used in the manufacture of milk glass,...

John Cancalosi / Duftite (Lead-calcium / copper-zinc arsenate hydroxide) on Calcite, an oxidation product of weathered ore deposits. Tsumeb, Namibia

John Cancalosi / Green fluorite (CaF2, calcium fluoride) a halide mineral. Fluorite is one of the most popular minerals among collectors and is used as a source of fluorine, in the manufacture of milk glass, as a flu...

John Cancalosi / Calcite (Calcium carbonate, CaCO3). One of the most common and variable minerals on earth, used in building, metallugy, fertilisers and the chemical industry. Juchem Quarry, Idar-Oberstein, Hunsruck M...

John Cancalosi / Calcite (Calcium carbonate, CaCO3) with haematite inclusions causing red colour. One of the most common and variable minerals on earth, used in building, metallugy, fertilisers and the chemical indust...

John Cancalosi / Calcite (Calcium carbonate, CaCO3). One of the most common and variable minerals on earth, used in building, metallugy, fertilisers and the chemical industry. Auglaize Quarry, Junction, Ohio. USA

John Cancalosi / Stilbite (hydrated sodium calcium aluminosilicate) a member of zeolite group. Used to separate hydrocarbons in petroleum refining. India

John Cancalosi / Selenite (CaSO4-2H2O) (Hydrous calcium sulphate) a form of Gypsum, from Mexico, formed in evaporite deposits

John Cancalosi / Fluorite (CaF2 - calcium fluoride), a halide mineral popular among collectors, used in aluminium refining, the steel industry and the manufacture of milk glass.

John Cancalosi / Creedite crystals [Ca3Al2SO4(F,OH)10-2(H2O) Calcium aluminium sulfate fluoro hydroxide] from Mina Navidad, Mexico, a popular mineral for collectors

John Cancalosi / Fluorite (CaF2 / calcium fluoride) crystals, from China, Fluorite is a source of fluorine used in the manufacture of milk glass, as a flux for the steel industry and in refining aluminum.

John Cancalosi / Fluorite crystals (CaF2 / calcium fluoride) source of fluorine used in the manufacture of milk glass, as a flux for the steel industry and in refining aluminum

John Cancalosi / Aragonite crystals (Ca CO3 / Calcium carbonate) from China

John Cancalosi / Fluorite crystals (CaF2 / Calcium fluoride) from Riemvasmaak, Northern Cape, South Africa. A source of fluorine, used in the manufacture of milk glass, as a flux for the steel industry and in refini...

John Cancalosi / Fluorite crystals (CaF2 / Calcium fluoride) from Riemvasmaak, Northern Cape, South Africa. A source of fluorine, used in the manufacture of milk glass, as a flux for the steel industry and in refini...

John Cancalosi / Calcite crystal on Amethyst. Calcite [Ca Co3 / Calcium Carbonate] one of the most common minerals on Earth. Amethyst [Sio2 / Silicon dioxide] a form of Quartz, the most common mineral on Earth

John Cancalosi / ScScheelite crystal [CaWO4] (below) on Muscovite, from China. Scheelite is calcium tungstate usually with some of the tunsten replaced by molybdenum, it is fluorescent and an important ore of tungsten...

John Cancalosi / Scheelite crystal [CaWO4] (below) on Muscovite, from China. Scheelite is calcium tungstate usually with some of the tunsten replaced by molybdenum, it is fluorescent and an important ore of tungsten,...

Graham Eaton / Aragonite, calcium carbonate, CaCO3, from the Yorkshire Dales, UK