https://www.esci.umn.edu/courses/1001/ minerals/dolomite.shtml Dolomite Carbonate Minerals
Chemical Composition
CaMg(CO3)2 Calcium Magnesium Car!onate. "ron ma# su!stitute $or some o$ o$ the magnesium.
C o l o r %ransparent to translucent cr#stals are t#picall# colorless& white& gra# or pin'& !ut i$ iron impurities are present can !e red& !rown or een !lac'. "n massie $orm& dolomite is t#picall# !u$$& gra#& or white. Cleavage
er$ect cleaage in three directions to produce rhom!ohedra
Hardness
3.* + (relatiel# so$t)
Specific Gravity
2.,* ($eels relatiel# light) to 3 in ironrich samples
L u s t e r Cr#stals are itreous (glassli'e) to pearl#& massie $orm is dull Streak Misc. Properties
-hite $$e $$er res esces ces (!u!! (!u!!le les) s) wea' wea'l# l# onl# onl# with with heat heated ed dilu dilute te acid acid&& or with with room room temperature dilute acid i$ dolomite is $irst crushed into a $ine powder to increase its sur$ace area. Often confused with...
Did #ou 'no w. w... .. Dolomite is one o$ our maor sources $or the concrete so essential to modern societ#s road and !uilding in$rastructure. Cr#stals o$ dolomite are common in
h#drothermal ein deposits and in sedimentar# roc's& where the# $ill pores in their host roc'. # olume& howeer& most dolomite occurs in its massie $orm as dolostone or mied dolostone/limestone sedimentar# roc's. %hese dolostone roc's originall# $ormed as limestone marine deposits on ancient shallow sea$loors that were later altered to dolostone as magnesiumrich waters moed through them. Dolostones that $ormed $rom the alteration o$ limestone roc' can retain much o$ the roc's original depositional tetures& such as $ossils& !edding& and other sedimentar# $eatures& although sometimes all o$ this original $a!ric was lost as the roc' recr#stallied.
Description and "denti$#ing Characteristics Most o$ten $ound as a massie& white to !u$$ or gra#& car!onate roc'$orming mineral& dolomite is one o$ the three most a!undant car!onate minerals& calcite and aragonite !eing the other two. Dolomite di$$ers $rom calcite and aragonite in its cr#stal structure. "n dolomite cr#stals& la#ers o$ car!onate ions alternate with la#ers o$ magnesium and calcium ions& rather t han onl# haing la#ers o$ calcium ions alternate with car!onate ions as in calcite and aragonite. Dolomite cr#stals usuall# $orm transparent to translucent rhom!s that are colorless to light colored& although cr#stals ma# !e red to !rown i$ iron impurities are present. 4ome dolomite cr#stals also ehi!it cr#stal $aces that $orm slightl# cured sur$aces& rather than $lat planes. ure samples o$ dolomite and calcite ma# hae a similar appearance and share man# properties& so the easiest wa# to distinguish them is !# their reaction with room temperature dilute acid. Calcite (and aragonite) will readil# react with acid to $orm small !u!!les (e$$erescence). Dolomite will onl# e$$eresce i$ the mineral is ground up into powder (or i$ the acid is heated). 5n$ortunatel#& natural massie samples o$ten consist o$ a miture o$ the two minerals& so it is sometimes di$$icult to distinguish whether dolomite is present in a mied massie sample. "ron ma# also su!stitute $or some o$ the magnesium in dolomite& so dolomite ma# grade into siderite& an iron car!onate (6eCO3)& although dolomite is $ar more a!undant than siderite. 7 %op
"n Our arth: %he 8eologic "mportance o$ Dolomite Dolomite $orms in h#drothermal eins or as a pore$illing mineral in car!onate roc's& and more rarel# as an accessor# component in igneous pegmatites or altered ma$ic igneous roc's. # $ar though& most dolomite occurs in altered sedimentar# marine roc's called dolostones or in mar!les $ormed $rom the metamorphism o$ dolostone. ecause dolostones are composed primaril# o$ the mineral dolomite& geologists once used the term 9dolomite $or !oth the mineral and the roc'. %he term is now onl# used $or the mineral& since a dolostone ma# include other minerals !esides dolomite. 6ew dolostones are primar# in origin. "n other words& the# did not originall# $orm as dolostone& !ut instead $ormed $rom the alteration o$ limestone roc' as magnesiumrich water moed through the limestone& altering its calcite and aragonite into dolomite. %he main eception to this is primar# dolomite that $orms in eaporitic settings as a relatiel# late product o$ seawater eaporation. %hese primar# dolomites are rare though. One o$ the more unusual primar# occurrences o$ dolomite (where dolomite is precipitated directl# $rom a $luid& rather than $orming as an alteration o$ a preeisting mineral) occurs in the
'idne#s o$ Dalmatian dogs "t appears this geologic peculiarit# is uni;ue to Dalmatians& as other dogs do not precipitate dolomite 'idne#. 4econdar# sedimentar# dolomites can !e !roadl# separated into two in$ormal groups. Man# sedimentar# dolomites occur $rom alteration o$ calcite and aragonite relatiel# soon a$ter their own $ormation& resulting in regionall# etensie masses o$ !edded dolostone. Other secondar# sedimentar# dolomites $orm $rom alteration o$ calcite and aragonite long a$ter these minerals had originall# $ormed. %hese latter dolomites tend to $orm dolostone masses along $ractures and $aults that sere as pathwa#s $or magnesium!earing $luids that altered the calcite and aragonite deposits. %he resulting dolostone tends to cut across the roc's original !edding rather than $ollow the !edding teture. "n !oth groups& the alteration o$ calcite and aragonite to dolomite ma# !e er# selectie. 6ossils composed o$ pure calcite ma# !e less li'el# to !e altered and ma# remain as calcite $ossils in an otherwise dolomite roc'.
"n Our 4ociet#: %he conomic "mportance o$ Dolomite Dolomite shares a !roadl# similar chemistr# with other car!onate minerals li'e calcite and aragonite& and conse;uentl# is used in much the same wa#. # olume& the most important uses o$ dolomite are in the production o$ concrete and as aggregate construction material. 4igni$icant amounts o$ dolomite are also used as dolostone and dolomitic mar!le !uilding stones and in the manu$acture o$ glass and ceramic glaes. "n industr#& dolomite is an important source $or magnesium and calcium metals& and is used as a $lu $or metallurg#. < $lu is a material that melts easil# and can !e used to remoe impurities $rom metal ores or to ma'e the slag produced !# metal ore smelting more $luid so it can !e disposed o$ more easil#. "n agriculture& powdered dolomite is also an important component o$ man# $ertiliers and animal $eeds. 4maller amounts o$ dolomite are also used $or human consumption as a mineral supplement and as an antacid& although to a lesser degree than calcite. Dolomite is een used in $acial creams and toothpaste. 5suall# minerals are named a$ter a $amous geographic localit# where the# occur& !ut dolomite was named $or a 6rench geologist named Deodat de Dolomieu (1>*01,01) who $irst identi$ied its chemical composition& and whose
scienti$ic career had a rather inauspicious !eginning. Deodat de Dolomieus earlier choice o$ a militar# career came to an a!rupt end a$ter he was condemned to death at the age o$ eighteen $or 'illing a $ellow soldier in a duel. ?e was pardoned& !ut decided to spend the remainder o$ his li$e pursuing roc's and minerals rather than militar# glor#. One o$ the areas where he wor'ed was a mountain range in northeastern "tal# that was later christened the 9Dolomites a$ter Deodat de Dolomieu. 7 %op
Dolomite in the 5pper Midwest: Dolomite is a!undant throughout most o$ the upper Midwest& !eing the primar# mineral comprising most o$ the aleooic car!onate units that coer this region. %housands o$ ;uarries in these roc' units proided the !ul' o$ the car!onate used locall# $or concrete in !uilding and road construction. One o$ the more common& relatiel# inepensie !uilding stones used in the region is a porous dolostone 'nown !# the geologicall# incorrect la!el o$ 9-inona %raertine. < true traertine is a porous car!onate roc' that is precipitated $rom groundwater at a spring or in a cae. "n contrast& the 9-inona %raertine is a dolostone that $ormed as an alteration o$ a marine limestone. "ts pores are the oid spaces le$t !# the dissolution o$ calcite $ossils and $ragments. %race $ossils o$ !urrowing organisms also etend throughout this dolostone& giing it a decoratie pattern that increases its worth as !uilding stone.
DOLOMITE
Chemistry: CaMg(CO3)2, Calcium Magnesium Carbonate Class: Carbonates Group: Dolomite Uses: in some cements, as a source of magnesium an as mineral specimens! "pecimens
Dolomite, which is named for the French mineralogist Deodat de Dolomieu, is a common sedimentary rock-forming mineral that can be found in massie beds seeral hundred feet thick! They are found all oer the world and are "uite common in sedimentary rock se"uences! These rocks are called a##ro#riately
enough dolomite or dolomitic limestone! Dis#utes hae arisen as to how these dolomite beds formed and the debate has been called the $Dolomite %roblem$! Dolomite at #resent time, does not form on the surface of the earth& yet massie layers of dolomite can be found in ancient rocks! That is "uite a #roblem for sedimentologists who see sandstones, shales and limestones formed today almost before their eyes! 'hy no dolomite( 'ell there are no good sim#le answers, but it a##ears that dolomite rock is one of the few sedimentary rocks that undergoes a significant mineralogical change after it is de#osited! They are originally de#osited as calcite)aragonite rich limestones, but during a #rocess call diagenesis the calcite and)or aragonite is altered to dolomite! The #rocess is not metamor#hism, but something *ust short of that! Magnesium rich ground waters that hae a significant amount of salinity are #robably crucial and warm, tro#ical near ocean enironments are #robably the best source of dolomite formation! Dolomite in addition to the sedimentary beds is also found in metamor#hic marbles, hydrothermal eins and re#lacement de#osits! E+ce#t in its #ink, cured crystal habit dolomite is hard to distinguish from its second cousin,calcite! ut calcite is far more common and efferesces easily when acid is a##lied to it! ut this is not the case with dolomite which only weakly bubbles with acid and only when the acid is warm or the dolomite is #owdered! Dolomite is also slightly harder, denser and neer forms scalenohedrons calcite#s most ty#ical habit.! Dolomite differs from calcite, CaCO3, in the addition of magnesium ions to make the formula, CaMg(CO3)2! The magnesium ions are not the same si/e as calcium and the two ions seem incom#atible in the same layer! In calcite the structure is com#osed of alternating layers of carbonate ions, CO3, and calcium ions! In dolomite, the magnesiums occu#y one layer by themseles followed by a carbonate layer which is followed by an e+clusiely calcite layer and so forth! 'hy the alternating layers( It is #robably the significant si/e difference between calcium and
magnesium and it is more stable to grou# the differing si/ed ions into same si/ed layers! Other carbonate minerals that hae this alternating layered structure belong to the Dolomite 0rou#! Dolomite is the #rinci#le member of theDolomite Group of minerals which includes an$erite, the only other somewhat common member! Dolomite forms rhombohedrons as its ty#ical crystal habit! ut for some reason, #ossibly twinning, some crystals cure into saddlesha#ed crystals! These crystals re#resent a uni"ue crystal habit that is well known as classical dolomite! 1ot all crystals of dolomite are cured and some im#ressie s#ecimens show well formed, shar# rhombohedrons! The luster of dolomite is uni"ue as well and is #robably the best illustration of a #early luster! The #earl-like effect is best seen on the cured crystals as a sheen of light can swee# across the cured surface! Dolomite can be seeral different colors, but colorless and white are ery common! 2oweer it is dolomite3s #ink color that sets another uni"ue characteristic for dolomite! 4rystals of dolomite are well known for their ty#ical beautiful #ink color, #early luster and unusual crystal habit and it is these clusters that make ery attractie s#ecimens! %256I47L 427874TE8I6TI469 •
Color is often #ink or #inkish and can be colorless, white, yellow, gray or een brown or black when iron is #resent in the crystal!
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%uster is #early to itreous to dull!
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&ransparency crystals are trans#arent to translucent!
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Crystal "ystem is trigonal& bar :
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Crystal 'abits include saddle sha#ed rhombohedral twins and sim#le rhombs some with slightly cured faces, also #rismatic, massie, granular and rock forming! 1eer found in scalenohedrons!
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Cleaage is #erfect in three directions forming rhombohedrons!
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racture is conchoidal!
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'arness is :!;-<
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"pecific Graity is =!>? aerage.
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"trea$ is white!
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Other Characteristics: @nlike calcite, efferesces weakly with warm acid or when first #owdered with cold 24l! *ssociate Minerals: include calcite, sulfie ore minerals, fluorite, barite, +uart and occasionally with gol! -otable Occurrences include many localities throughout the world, but well known from sites in Midwestern "uarries of the @67& Ontario, 4anada& 6wit/erland& %am#lona, 6#ain and in Me+ico! .est iel /nicators are ty#ical #ink color, crystal habit, hardness, slow reaction to acid, density and luster!
Calcite (and
Chemical Composition
Calcium Car!onate: Ca(CO3)& Mn& 6e& Mg and 4r ma# partiall# replace Ca in some samples.
C o l o r %ransparent to translucent calcite cr#stals are colorless& white or lightcolored@ massie $orms o$ calcite are t#picall# !u$$& gra#& or white. Cleavage
Calcite has per$ect cleaage in three directions to produce rhom!ohedra. (Cleaage in aragonite is generall# less well deeloped.)
Hardness
3 (down to 2.* on some sur$aces) A easil# scratched !# a metal nail& !ut too hard to !e scratched !# a $ ingernail.
Specific Gravity
2.> ($eels relatiel# light) (3.0 $or aragonite)
L u s t e r cr#stals are itreous (glassli'e)& massie $orm is dull Streak Misc. Properties
white
Did #ou 'no w... -ithout calcite and aragonite man# o$ arths organisms could not eist. %hese are the minerals most inerte!rate organisms use to construct their shells and hard parts. 4o i$ #ou hae eer admired a color$ul seashell& #ou hae alread# paid tri!ute to the range o$ colors calcite and aragonite come in and indirectl# to the ease with which calcite and aragonite $orm at the arths sur$ace.
Description and "denti$#ing Characteristics Calcite occurs in !oth cr#stalline and massie $orms. Cr#stals o$ calcite are usuall# transparent to translucent& !ut can ehi!it a wide ariet# o$ colors i$ the cr#stal includes minor impurities. Masses o$ calcite also tend to !e light colored&
!ut as with the transparent cr#stals& the presence o$ een minor amounts o$ impurities can create a wide range o$ colors. 4ince calcite can hae so man# appearances& the simplest wa# to determine whether a sample contains calcite is to test its reaction to a dilute acid li'e household inegar. Calcite will readil# react with acid to 9e$$eresce& producing small !u!!les o$ CO2 similar to those $ormed when #ou open a !ottle o$ soda and pour it into a glass. 4o$t enough to !e easil# scratched !# a nail& calcite cr#stals can also !e identi$ied !# their rhom!ic cleaage. 9Bhom!ic cleaage means that calcite cr#stals !rea' along parallel planes o$ wea'ness that meet at the same angles as a rhom!s sides. 7 %op
8eologic 4etting and
"n Our arth: %he 8eologic "mportance o$ Calcite
"n Our 4ociet#: %he conomic "mportance o$ Calcite %he ease with which it dissoles and precipitates is the !asis $or man# o$ calcites uses in human societ#. Calcites name comes $rom 9chali or 9chal& which is the 8ree' word $or lime (9cal in atin). 6or oer *&000 #ears& calcite has !een used to manu$acture lime (CaO& calcium oide).
remains the same. Boc's rich in calcium car!onate are heated to high temperatures so the CaCO3 will !urn to $orm CaO and CO2 gas. %he CaO can then !e recom!ined with water (which alwa#s holds some dissoled CO2) to precipitate CaCO3 as plaster& mortar& and more recentl# as cement. arl# Boman and 8ree' $rescos attest to the use o$ lime in art as well.
Calcite in the 5pper Midwest: "n the 5pper Midwest region& calcite and dolomite are the most important minerals that comprise the car!onate roc' la#ers that coer the regions southeastern etent. %hese roc's are ;uarried $or use as !uilding stones and as grael $or road construction. Marl& a miture o$ calcite and cla# minerals& $orms !eneath man# o$ the states la'es and wetland areas. =ein deposits o$ calcite
occur in man# regional roc' units& !ut are particularl# common in the !asalts and ga!!ros that $orm the Forth 4hore o$ a'e 4uperior. Calcite and aragonite also $orm most o$ the cae decoration $ound in caerns present within the car!onate roc' units across the southern part o$ this region. "n 5pper Midwest caes& calcite is the primar# mineral component o$ cae $ormations such as stalactites and stalagmites& although man# o$ the more delicate cae $eatures are composed o$ aragonite. On a more domestic $ront& calcite is the mineral that dissoles to $orm the 9hard water (water with high concentrations o$ dissoled ions) present in man# 5pper Midwest communities. "n homes without water so$teners& calcite can precipitate $rom calciumrich groundwater to plug household plum!ing or $orm a crust !elow dripping $aucets. 7 %op
"n Our 6uture: %he nironmental "mplications o$ Calcite 5s e Car!on dioide is a greenhouse gas that traps heat radiated $rom the arth to warm the arths sur$ace. Fatural emissions o$ car!on dioide $rom olcanoes and plants warm the arth so that it is not a $roen planet. ?oweer& as human actiities increase the leels o$ CO2 in the atmosphere& we run the ris' o$ changing the arths climate !# increased greenhouse warming.
