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。
Medium hard formation with high compressive strength. Such as hard shale, limestone, sandstone, dolomite, anhydrite and marble.
我要做的就是，选择一块够硬的石锤，这次我选这块是个头有板球大小的石英岩卵石。先挑个地方锤下去，接着我就开始从这地方开始凿了。
And what I do is, I select a hard stone hammer, in this case a quartzite pebble about the size of a cricket ball, and I elect to hit it in one place - and this is where I start to knap.
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