This rock specimen is a beautiful pink marble from a gold bearing zone in Northeastern Ontario. Normal marble forms by the recrystallization of the limestones carbonate minerals calcite CaCO3 or dolomite CaMg(CO3)2. This marble is different. It formed by the alteration of an ultramafic volcanic rock by the addition of CO2 to Ca-Mg-Fe silicates to form iron rich dolomite Ca(Mg,Fe)(CO3)2 and quartz SiO2. This rock has an interesting history. Approximately 8,000 years ago glaciers melted exposing fresh unaltered rocks in the Kirkland Lake gold belt.
This rock was exposed in exploration trenching of shallow overburden near a hill top. 8,000 years, this rock, weakly acid rain water dissolved 2 centimeters of dolomite. The dolomite neutralized the acid water.
The acid in the rain water dissolved the marble at a rate of 1 mm every 400 years.
In many rocks, acid rain causes pyrite FeS2 to weather forming sulfuric acid which cause the water to become more acidic which can cause heavy metals to be leached into the ground water.
Locally this type of marble has fine disseminated pyrite grains. This this marble neutralizes acid rain, this pyrite survives as fresh pyrite within the brown weathering rind.
High lime, limestone is a favored rock to neutralize plumes of acid drainage acid from natural and industrial sites including mines. This rock is initially the best rock to neutralize acidic water; however there is a problem. Limestone slimes over removing the limestone from contact with the acid it was intended to neutralize. If this in in an acidic ground water plume it ceases to function.
It appears siliceous iron rich marble may form a porous shell that prevents slimming from isolating the marble from acid waters. If this prove to be true, large volumes of this rock are available for environmental applications. In addition it could create a valuable environmental tool from mine waste rock.
This is the type of story this website intends to use to spark interest mineral and rock collectors into understanding their hobby more fully.