ABSTRACT

Experimental pressure solution of quartz was conducted in hydrothermal reactors. Loads ranged from 2500 psi to 12,000 psi, with temperatures ranging from 270°C to 550°C. Pressure solution occurred in distilled water as well as in solutions of NaOH, Na₂CO₃, NaCl, and natural brines. Clearly defined pressure solution pits were readily observed on faces of quartz crystals which had been surrounded by small zircon grains and subjected to load.

The rate of compaction of fine sand was much greater than that of coarse sand, resulting in a pore space reduction of 70 percent in fine sand compared to a 45 percent reduction in coarse sand. The rate of compaction of fine angular sand was approximately 2.3 times that of fine round sand. As a result of pressure solution and growth, the appearance of the angular grains was little different from that of the round grains after comparable pressure solution. Simultaneous pressure solution and quartz growth in sand samples produced aggregates which were considerably stronger than those resulting from cementation alone.

Samples composed of grains of chert responded to pressure solution much more rapidly than monocrystalline quartz. The chert did not completely recrystallize, but grain boundaries became very indistinct and the resulting product resembled a solid mass of chert.

The experimental studies show that as a result of pressure solution, initial differences in texture and composition of natural sands may lead to striking differences in final porosity.