To prepare a petrographic thin section from a rock sample, geologists follow a precise sequential protocol. First, the raw rock specimen is cut into a small, rectangular block using a diamond-tipped saw. Before mounting the block onto a glass slide, the cut surface must be ground flat with progressively finer silicon carbide abrasive grits. This grinding step is critical: it removes saw marks and ensures a completely planar surface. Once the surface is polished, the block is thoroughly cleaned in an ultrasonic bath and dried on a hot plate to eliminate any moisture or debris that could impede adhesion. Subsequently, the dried block is bonded to a clean glass slide using an epoxy resin, which is then left to cure under pressure for twelve hours. After curing, the excess rock is sliced off with a thin-section cut-off saw, leaving a slice approximately thick. Finally, the remaining rock layer is ground down to the standard thickness of () using a precision lapidary wheel, allowing light to pass through the mineral crystals during microscopic analysis.
According to the passage, what is the direct consequence of omitting the grinding step that occurs prior to mounting the rock block onto the glass slide?
- AThe mineral crystals would remain completely opaque under the microscope during final analysis.
- The rock block would be bonded to the glass slide with saw marks still present on the contact surface.Answer
- CResidual moisture and debris on the block's surface would prevent the epoxy resin from adhering properly.
- DThe rock block would be too thick to be cut by the thin-section cut-off saw after curing.