kuyini ukhuni olujiyile
Context:Ukhuni olujiyile, olwaziwa nangokuthi isihlahla esijiyile (kusuka esiGrekini sasendulo πέτρα okusho ukuthi 'idwala' noma 'itshe'; ngokwezwi nezwi 'ukhuni oluphenduke itshe'), yigama elinikezwe uhlobo olukhethekile lokhuni olujiyile, izinsalela ezijiyile zezitshalo zasemhlabeni. Ukugqwala kuwumphumela wokushintshwa kwesihlahla noma izitshalo ezifana nesihlahla ngamatshe ngenqubo yokwakheka kwamaminerali okuvame ukuhlanganisa ukuguqulwa kwamaminerali nokufakwa esikhundleni sawo. Izinto eziphilayo ezakha izindonga zamangqamuzana ziye zaphindwa ngamaminerali (ikakhulukazi i - silica ngesimo se - opal, i - chalcedony, noma i - quartz). Kwezinye izimo, isakhiwo sangempela sesikhumba singase silondolozwe ngokwengxenye. Ngokungafani nezinye izinsalela zezitshalo, ngokuvamile eziwumphumela wokudwetshwa noma ukucindezelwa, ukhuni olujiyile luwumfanekiso onezinhlangothi ezintathu wezinto eziphilayo zokuqala.  Inqubo yokwakheka kwamatshe yenzeka ngaphansi komhlaba, lapho izinkuni zingcwatshwa emanzini noma ematsheni entaba-mlilo. Ukuba khona kwamanzi kunciphisa ukutholakala komoya-mpilo okuvimbela ukubola kwe-aerobic ngama-bacterium nesikhunta. Amanzi agcwele amaminerali agelezela phakathi kwezinsalela angaholela ekwakhekeni kwamaminerali angapheli, okwenzeka lapho amaminerali ehla ngaphandle kwesixazululo agcwalisa ingaphakathi lamaseli nezinye izindawo ezingenalutho. Phakathi nokubuyiselwa, izindonga zamangqamuzana ezitshalo zisebenza njengethempulethi yokwakheka kwamaminerali. Kudingeka kube nokulinganisela phakathi kokubola kwe - cellulose ne - lignin nokwakheka kwamaminerali ukuze imininingwane yamangqamuzana ilondolozwe ngokwethembeka. Iningi lezinto eziphilayo livame ukubola, kodwa ezinye ze-lignin zingase zihlale. I-silica ngesimo se-opal-A, ingakwazi ukugxila futhi igcwale izinkuni ngokushesha okukhulu ezindaweni ezinemithombo eshisayo. Nokho, ngokuvamile izinkuni eziphenduke amatshe zihlobene nezihlahla ezazingcwatshwe emanzini amancane asezindaweni ezivulekile noma ezivulekile noma emibhedeni yomlotha. Ihlathi lapho impahla enjalo iye yaqina khona liyaziwa ngokuthi ihlathi eliqinile.
Ukhuni olujiyile lungelinye lamafosili, luyisitshalo ingxenye yaso yangaphakathi eye yathathelwa indawo itshe ngokucindezelwa kanye nemidwebo phakathi nezigidi zeminyaka