Medium hard formation with high compressive strength. Such as hard shale, limestone, sandstone, dolomite, anhydrite and marble.

高抗压强度的中硬地层，如硬页岩。石灰岩。砂岩。白云岩。和硬石膏。大理石。

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Cementation is showed by the secondary enlargement of quartz and feldspar, the successive formation and pores filling of cementing material of authigenic clay mineral, calcite and anhydrite, etc.

胶结作用表现为石英和长石的次生加大、自生粘土矿物、碳酸盐和硬石膏胶结物的依次形成并充填孔隙。

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