Update on Snowmom's Impactite Specimens

Think about how you'd dissolve something. Say sugar... in a nutshell, most chemicals dissolve better with heating.

The calcite family (lime, calcium carbonate & aragonite) for whatever reason does the opposite.

With cooler temperatures at night, the shelly sands dissolve. As the day light warms the shallow seas in and around reefs, the sea has too much dissolved calcite and it has to come out of solution so it sticks on a microscopic, molecular level to any existing grains. Repetition, day in, day out and the layers build up around a 'seed' centre: what you have is essentially a mini calcite gobstopper.

Imagine, all the grains on a beach or length of coast doing this until they're buried. Once they're packed in, underneath lots of others they are effectively insulated and with less change in temperature, there's less opportunity for the minerals to move; essentially their development is halted. All the grains have 'enjoyed' the same life-cycle, hence they're all the same: similar grain 'seed' centres and roughly the same number of laminations and so, preserved to the present day, they are essentially 'identical', except to the microscopic evaluation.

HTH