Final answer:
The question concerns oolite, a type of limestone composed of sand-sized calcite spheres known as ooliths, which forms in warm, shallow waters and fizzes when exposed to dilute hydrochloric acid (HCl) due to the reaction with calcite.
Step-by-step explanation:
The subject of the question is a type of limestone known as oolite. Limestone is a sedimentary rock primarily composed of the mineral calcite (calcium carbonate), which can form in various ways, including biologically and chemically.
Oolite, specifically, consists of sand-sized calcite spheres, known as ooliths, that develop concentric layers in shallow, wave-agitated environments such as warm shallow waters.
These spheres cement together to form the rock. When limestone is exposed to dilute hydrochloric acid (HCl), it effervesces, or fizzes, due to the reaction between the acid and the calcite releasing carbon dioxide gas.
This characteristic fizzing reaction is a key test in identifying calcium carbonate-based rocks and minerals.
Some limestone contains chert, a very hard form of silica that can weather to brown and form nodules or even replace fossil shells. In addition to oolite, other formations such as calcareous tufa and chalk are also types of calcium carbonate sediments that commonly reacts with acids.