earthscienceguy: Minnesota Geology Monday

St. Cloud has the nickname “The Granite City” for good reason.  There were almost one hundred granite quarries in the area over time, but currently there are four in operation in towns like Cold Spring, Rockville and St. Cloud.  Numerous granite plutons are found in the region, together they are known as the East-Central Batholith.  The individual granite plutons have also been informally named, including the Richmond, Rockville and St. Cloud Red, among others.  Radiometric ages of the granites range from 1,800 to 1,750 million years.

The granite is quarry in the area by several company for use as either dimension stone or aggregate .  

Cold Spring Granite

maintain several quarry and a processing plant for decorative use on building , countertop , headstone , etc .   The quarry is are picture here are from the Rockville Quarry # 2 , which is sell by the tradename

Rockville White

. 

Located just above the granite in the area, and seen well in many quarries, are rounded boulders of granite.  These are corestones.  The granites in the area are jointed, weathering of the granite affect the corners of the joints first, eventually smoothing the corners and producing rounded boulders.  The weathering event most likely took place during the Cretaceous, the same period which formed the kaolinite clays found in the upper Minnesota River Valley.

The region is also swarm by many diabase intrusion .   These intrusion are easily see within the

Martin Marietta

aggregate quarry .

Below is a picture of me standing in front of a diabase dike intruding on a body of St. Cloud Red granite.

Because quarry are privately own and a potential safety hazard , explore them without guidance or permission is not allow .  

Quarry Park and Nature Reserve

is a public park that allows easy access to many of the features found within the granite throughout the region.  Like the name suggests, the area was once home to almost 30 granite quarries.

The granite present in the park is known as the St. Cloud Red granite.  Most of the former quarries are now filled with water, one is used as a swimming pond that is 112 feet deep.  There are also large piles of quarried rock found throughout the park.

Walking the many hiking trails within the park, it’s easy to examine the relationship between the granite and diabase intrusions.

Upon closer inspection, you are also able to find places where pieces of granite were broken off by the intruding magma.  These inclusions of granite are now frozen within the diabase intrusion.