Anhydrite has not been a widely popular stone, but its availability on the west coast of North America and the beauty of its finish are likely to result in more sittings in sculpture exhibits in the future. It has the pearly luster of alabaster and yet carves and finishes more like harder stone.
Anhydrite is both a mineral and a sedimentary rock. Its name comes from the Greek for “without water:” essentially it is the anhydrous form of calcium sulfate (CaSO4). Anhydrite is the sister or brother of alabaster (gypsum), which is the hydrated form of calcium sulfate (CaSO4: 2H2O). Two molecules of water are attached to each molecule of calcium sulfate in gypsum.
Anhydrite commonly is found in white, gray, brown, and light red, or pink. It is heavier than alabaster, weighing in at about 187 pounds per cubic foot with a specific gravity of 3.0. One of the key differences between alabaster and anhydrite is the hardness: alabaster is 2 and anhydrite ranges from 3 to 3.5. It is insoluble in hydrochloric acid and sulfuric acid; however, it is easily attacked by water. In the earth, anhydrite converts to gypsum when it absorbs water, and in your yard it will break down with facility, if exposed to the elements.
Anhydrite is one of a group of rock-forming minerals called evaporites, so called because they form by the precipitation of the minerals from evaporating brines or salt water. The other evaporites are gypsum and halite (salt). They form in shallow salt water seas that are alternately submerged and dewatered. Beds of the rock can be found in thicknesses of a few feet to hundreds of feet. Which mineral is precipitated at any time depends on the temperature, pressure, and salinity of the water. At higher temperatures, anhydrite is the first one to precipitate, followed by gypsum; however, at lower temperatures, the opposite is the case. Halite is normally the last to form. In the laboratory, and presumably in nature, gypsum and anhydrite can be made to convert to one another by the changing of pressure and temperature. It is also known that anhydrite can be changed to gypsum by the addition of water, such as during the weathering process. Conversely, the reverse can be achieved by the baking or drying of gypsum.
In North America, anhydrite is found in the salt domes of Louisiana and Texas and in stratified deposits in Nova Scotia, New York, New Mexico, and British Columbia. It is also in large layered salt deposits of Poland, Germany, Austria, France, and India. Anhydrite is not considered an important industrial mineral and is treated as a contaminant in large deposits of gypsum. It is used as a source of sulfuric acid, as a retardant for concrete curing, for a filler in paper, and as a soil conditioner.
Although anhydrite is relatively hard stone, it is somewhat easy to mine because it is naturally broken by numerous joints. This makes mining anhydrite, for sculpture, easily done without blasting, which would shatter and make unusable much of the stone. It is removed from the ground or rock face by hand tools or with a backhoe. The best method for determining the integrity of the stone is to tap the stone with a hammer and listen carefully for changes in the ring.
Anhydrite is brittle and hand tool working is not recommended. Although a hardness of 3 to 3.5 is not extreme, sculptors who have worked the stone definitely prefer power tools. Hand chisels tend to create small chips in the surface, and sharp corners are commonly lost when unexpected breaks occur. The good part is that anhydrite is unlikely to bruise, in the manner of alabaster. It can be worked with a hand-held grinder as well as a stationary wheel, and the stone cuts very evenly and easily with such tools. Anhydrite takes well to a grinder and carbide disks will show little wear after working the stone.
Anhydrite can be taken to a 70 to 600 grit finish, depending on the color and pattern of the stone, and buffed with tin oxide using a wet rag or a mechanical buffer. Of all the colors, the translucent white produces the most lustrous finish although, the brown may have the most interesting patterns.
Cracks and joints are not common flaws in anhydrite. In general, it is a solid stone. The white variety tends to be the most consistent in color and hardness, containing scattered soft spots. Sometimes, small white spots may be present in the stone.
Although not exactly a flaw of the stone, a major weakness of all anhydrite is its susceptibility to water. It must be kept indoors before and after carving. If left outdoors, it will absorb water and deteriorate.
No particular safety hazards are reported for anhydrite however, we all need to remember to protect our lungs, eyes, and ears at all times. Be a sage and safe sculptor.
Thanks to Randy Zieber of Vancouver, British Columbia for his quarrying and carving expertise and to Carol Way of Seattle, Washington and Vic Picou of Burbank, California for sharing their carving experiences with me.
Anhydrite haijawahi kuwa jiwe maarufu sana, lakini upatikanaji wake kwenye pwani ya magharibi ya Amerika ya Kaskazini na uzuri wa kumaliza kwake kuna uwezekano wa kusababisha viti zaidi katika maonyesho ya sanamu katika siku zijazo. Ina mng'ao wa lulu wa alabaster na bado huchonga na kumaliza zaidi kama jiwe gumu. Anhydrite ni madini na mwamba wa matope. Jina lake linatokana na Kigiriki kwa <unk> bila maji: <unk> kimsingi ni aina ya anhydrous ya kalsiamu sulfate (CaSO4). Anhydrite ni ndugu wa alabaster (gypsum), ambayo ni aina ya hydrated ya kalsiamu sulfate (CaSO4H2O). Molekuli mbili za maji zimeunganishwa na kila molekuli ya sulfati ya kalsiamu katika gypsum. Kwa kawaida anhydrite hupatikana kwa rangi nyeupe, kijivu, kahawia, na nyekundu nyepesi, au waridi. Alabaster ni nzito zaidi kuliko mawe ya mawe ya mawe ya mawe, na inazidi uzito wa kilo 187. Alabaster ni ngumu sana, lakini anhydrite ni ngumu sana. Ni insoluble katika asidi hydrochloric na asidi sulfuric; hata hivyo, ni kwa urahisi kushambuliwa na maji. Katika ardhi, anhydrite hubadilika kuwa gypsum wakati inachukua maji, na katika bustani yako itaharibika kwa urahisi ikiwa itafunuliwa kwa vitu vya asili. Anhydrite ni moja ya kundi la madini ya mwamba-kuunda evaporites, hivyo kuitwa kwa sababu wao kuunda kwa precipitation ya madini kutoka evaporating brines au maji ya chumvi. Vitu vingine vinavyotokana na mvuke ni gypsum na halite (chumvi). Wao hufanyizwa katika bahari zisizo na kina kirefu zenye maji ya chumvi ambazo hufunikwa na kutoweka maji kwa zamu. Vitanda vya miamba vinaweza kupatikana kwa unene wa meta chache hadi mamia ya mita. Ni madini gani yanayotiririka wakati wowote yanategemea halijoto, shinikizo, na chumvi ya maji. Katika joto la juu, anhydrite ni ya kwanza kutiririka, ikifuatiwa na gypsum; hata hivyo, katika joto la chini, kinyume ni kesi. Kwa kawaida halite hufanyizwa mwisho. Katika maabara, na labda katika asili, gypsum na anhydrite inaweza kufanywa kugeuka kwa kila mmoja kwa kubadilisha shinikizo na joto. Pia inajulikana kwamba anhydrite inaweza kubadilishwa kuwa gypsum kwa kuongeza maji, kama vile wakati wa mchakato wa hali ya hewa. Kinyume chake, kinyume cha hilo chaweza kupatikana kwa kuoka au kukausha gypsum. Katika Amerika Kaskazini, anhydrite hupatikana katika matope ya chumvi ya Louisiana na Texas na katika matope ya tabaka katika Nova Scotia, New York, New Mexico, na British Columbia. Pia inapatikana katika matope makubwa ya chumvi ya Poland, Ujerumani, Austria, Ufaransa, na India. Anhydrite haichukuliwi kuwa madini muhimu ya viwanda na hutendewa kama uchafuzi katika amana kubwa za gypsum. Inatumiwa kama chanzo cha asidi ya sulfuri, kama retardant kwa ajili ya saruji curing, kwa ajili ya kujaza katika karatasi, na kama conditioner udongo. Ingawa anhydrite ni jiwe gumu, ni rahisi kuchimba kwa sababu huvunjwa kwa njia ya asili na viungo vingi. Hii hufanya uchimbaji wa anhydrite, kwa ajili ya sanamu, kufanywa kwa urahisi bila kulipua, ambayo ingevunjika na kufanya usioweza kutumika zaidi ya jiwe. Inatolewa kutoka ardhini au kwenye mwamba kwa kutumia vifaa vya mkono au kwa kutumia mashine ya kuchimba. Njia bora ya kuamua uadilifu wa jiwe ni kugonga jiwe kwa nyundo na kusikiliza kwa makini kwa mabadiliko katika pete. Anhydrite ni dhaifu na kazi ya zana ya mkono haipendekezi. Ingawa ukali wa 3 hadi 3.5 si wa hali ya juu, wachongaji ambao wamefanya kazi na jiwe hilo hupendelea zana za umeme. Vipande vidogo vya mkono hufanyiza vipande vidogo kwenye uso, na kwa kawaida pembe kali hupoteza wakati mapumziko yasiyotarajiwa yanapotokea. Sehemu nzuri ni kwamba haiwezekani kwamba anhydrite ivute, kama vile alabaster. Inaweza kutengenezwa kwa mashine ya kusaga ya mkono na pia kwa gurudumu la kusimama, na jiwe hilo hupunguzwa kwa usawa na kwa urahisi sana kwa kutumia vifaa hivyo. Anhydrite inachukua vizuri kwa grinder na diski carbide itaonyesha kuvaa kidogo baada ya kufanya kazi ya jiwe. Anhydrite inaweza kuchukuliwa kwa 70 hadi 600 grit kumaliza, kulingana na rangi na muundo wa jiwe, na polished na tin oxide kwa kutumia kitambaa mvua au buffer mitambo. Kati ya rangi zote, nyeupe yenye kung'aa hutokeza rangi yenye kung'aa zaidi ingawa, rangi ya kahawia huenda ikawa na michoro yenye kupendeza zaidi. Mvunjiko na viungo si kasoro za kawaida katika anhydrite. Kwa ujumla, ni jiwe imara. Aina nyeupe huwa na rangi na ugumu sawa, na ina madoa laini yaliyotawanyika. Nyakati nyingine, huenda ikawa na madoa madogo meupe kwenye jiwe hilo. Ingawa si kosa halisi la jiwe hilo, udhaifu mkubwa wa anhydrite yote ni uwezekano wake wa kuathiriwa na maji. Ni lazima ihifadhiwe ndani ya nyumba kabla na baada ya kuchonga. Ikiwa itaachwa nje, itachukua maji na kuharibika. Hakuna hatari maalum ya usalama kwa anhydrite, hata hivyo, sisi sote tunahitaji kukumbuka kulinda mapafu yetu, macho, na masikio wakati wote. Kuwa mchongaji mwenye hekima na salama. "Randy Ziebler, kutoka Vancouver, British Columbia, alishukuru kwa uzoefu wake wa kuchimba na kuchonga, na Carol Way, kutoka Seattle, Washington, na Vic Picou, kutoka Burbank, California, kwa kushiriki uzoefu wao wa kuchonga na mimi. """