Pumice cyangwa pumice ni ubwoko bwurutare rufite ibara ryoroshye, rurimo ifuro ikozwe mubirahuri bikikijwe nikirahure, kandi mubisanzwe byitwa ikirahuri cyibirunga.
Urutare rukorwa na magma acide nigikorwa cyo guturika kwikirunga gisohora ibintu mukirere; hanyuma unyure kuri horizontal hanyuma ukusanyirize hamwe nk’urutare rwa pyroclastique.
Pumice ifite imiterere ihanitse, irimo umubare munini wingirabuzimafatizo (imiterere ya selile) bitewe no kwaguka kwifuro ya gaze isanzwe irimo, kandi mubisanzwe usanga ari ibintu bidakabije cyangwa ibice muri breccia yibirunga. Mugihe imyunyu ngugu irimo pumice ari feldspar, quartz, obsidian, cristobalite, na tridymite.
Pumice ibaho iyo magma acide yazamutse hejuru igahita ihura numwuka wo hanze. Ikirahuri gisanzwe kirimo / gaze kirimo gifite amahirwe yo guhunga kandi magma irakonja gitunguranye, pumice muri rusange ibaho nkibice bisohoka mugihe kiruka cyibirunga bifite ubunini kuva mumabuye kugeza kumabuye.
Pumice ikunze kugaragara nko gushonga cyangwa gutemba, ibintu birekuye cyangwa ibice muri breccias yibirunga.
Pumice irashobora kandi gukorwa no gushyushya obsidian, kugirango gaze ihunge. Ubushyuhe bukorerwa kuri obsidian kuva Krakatoa, ubushyuhe busabwa kugirango uhindure obsidian muri pumice wagereranije 880oC. Uburemere bwihariye bwa obsidian bwahoze bugera kuri 2.36 bwamanutse kuri 0.416 nyuma yo kuvurwa, bityo bureremba mumazi. Iri buye rya pumice rifite hydraulic.
Pumice ni umweru kugeza imvi, umuhondo kugeza umutuku, imitsi ya vicicular hamwe nubunini bwa orifice, bigenda bitandukana hagati yabyo cyangwa ntabwo bihuye nimiterere yaka ifite icyerekezo.
Rimwe na rimwe umwobo wuzuyemo zeolite / calcite. Iri buye rirwanya ikime gikonje (ubukonje), ntabwo ari hygroscopique (amazi yonsa). Ifite ubushyuhe buke bwo kohereza. Imbaraga zingutu hagati ya 30 – 20 kg / cm2. Ibice nyamukuru bigize amorphous silicate minerval.
Ukurikije uburyo bwo gushinga (desposition), gukwirakwiza ingano yingingo (agace) nibikoresho byaturutse, kubitsa pumice byashyizwe muburyo bukurikira:
Agace
Amazi yo mu mazi
Ardante nshya; ni ukuvuga kubitsa byakozwe na horizontal isohoka ya gaze muri lava, bikavamo kuvanga ibice byubunini butandukanye muburyo bwa matrix.
Ibisubizo byo kongera kubitsa (reduposit)
Uhereye kuri metamorphose, gusa uduce dusa nibirunga bizagira ububiko bwa pumice. Imyaka ya geologiya yabibitse iri hagati ya Tertiary nubu. Ibirunga byakoraga muri iki gihe cya geologiya harimo inkombe y’inyanja ya pasifika n’inzira igana ku nyanja ya Mediterane igana Himalaya hanyuma ikerekeza mu Buhinde bw’Uburasirazuba.
Urutare rusa nizindi pumice ni pumicite na cinder cinder. Pumicite ifite imiti imwe, inkomoko yimiterere nikirahure nka pumice. Itandukaniro riri mubunini buke gusa, buto kuri santimetero 16. Pumice iboneka hafi yaho ikomoka, mugihe pumicite yatwarwaga numuyaga intera ndende, ikabikwa muburyo bwo kwegeranya ivu rinini cyangwa nkibishishwa bya tuff.
Ikirunga cy’ibirunga gifite ibara ritukura kugeza ibice byumukara, byashyizwe mugihe cyo guturika kwamabuye ya basaltike biturutse kumirunga. Byinshi mububiko bwa cinder buboneka nkibice byo kuryamaho kuva kuri santimetero 1 kugeza kuri santimetero nyinshi.
Ibishoboka bya Indoneziya
Muri Indoneziya, kuba pumice ihora ihujwe nuruhererekane rwa Quaternary to Tertiary ibirunga. Ikwirakwizwa ryayo rikubiyemo uduce twa Serang na Sukabumi (Uburengerazuba bwa Java), ikirwa cya Lombok (NTB) n’ikirwa cya Ternate (Maluku).
Ubushobozi bwo kubitsa pumice bufite akamaro mubukungu nububiko bunini cyane ni ku kirwa cya Lombok, West Nusa Tenggara, ikirwa cya Ternate, Maluku. Umubare wibigega byapimwe muri kariya gace ubarirwa kuri toni zirenga miliyoni 10. Mu gace ka Lombok, ikoreshwa rya pumice ryakozwe kuva mu myaka itanu ishize, naho muri Ternate iryo hohoterwa ryakozwe mu 1991 gusa.