Taw qhia rau Chalk

Chalk yog cov cuab yeej siv dav hauv lub neej niaj hnub, feem ntau siv rau kev sau ntawv rau ntawm cov ntawv dub. Ancient chalk feem ntau yog ua los ntawm ntuj chalk, tab sis tam sim no nws yog hloov los ntawm lwm yam tshuaj. Lub ntsiab ntawm chalk yog calcium sulfate, uas yog ib tug dawb precipitate, uas yog tsis yooj yim rau decomposed, thiab hais tias yog loj dua hmoov av. Cov chalks siv hauv Suav teb feem ntau suav nrog cov chalk thiab hmoov av-dawb chalk. Cov khoom tseem ceeb yog calcium carbonate (limestone) thiab calcium sulfate (gypsum), los yog ib qho me me ntawm calcium oxide.