Fact #21 Molten rock that cools at depth will form crystals.   As a general rule, the slower the cooling, the larger the crystals.   Compare the crystals found in the granite of the Landmark Center in downtown St. Paul to the crystals found at the Wells Fargo Tower a few blocks away.   At the Landmark Center, the crystals are smaller, which implies a faster cooling, and likely more the granite was formed closer to the surface of the earth.

Fact #22 Limestone, which is exposed to pressure and increased temperature, will metamorphose into Marble.   During the exposure to pressure, some of the limestone with dissolve and the material will be removed.   This will leave behind a squiggly line in the rock, called a styolite .   Styolites can be seen in the exterior marble of the St. Paul Public Library.

Fact #23 Sandstone is formed by the deposition of sand grains in moving water or air (sand dunes in a desert environment). When the fluid slows down, the heavier grains stop moving and are deposited.   Sand grains may be reworked by waves along a shoreline, which will winnow the size of the grains and remove clay particles.   The sand which formed the

St. Peter Sandstone was reworked for many years, cleaning out the clay material.  

The St. Peter is so clean that Ford Motor Company plant in St. Paul used the sandstone to make windshield glass for a number of years.

Fact #24 Sandstone buried underground by deposition of other rock layers above it will compact and make the rock hard (referred to as lithification ).   The St. Peter Sandstone, which can be seen at Daytons Bluff in St. Paul, was never buried very deeply, and thus never was compacted and lithified to a large degree.   Thus, the St. Peter Sandstone can be dug by hand in the St. Paul area.

Fact #25 Brownstone is a hard sandstone with a small quantity of hematite mixed in.   Hematite is an iron rich rock, which gives the sandstone the brown or reddish look.   Brownstone is used in several buildings in Downtown St. Paul and many residential houses in the Twin Cities area.

Fact #26 Examples of rocks found in Minnesota may be viewed on this website: http://www.geo.umn.edu/mgs/virt_egg/secondpg.htm

Fact #27 Minerals are defined as a structurally homogeneous solid with a definite chemical structure.   These are formed by inorganic (i.e. not the product of plants or animals) processes of nature.   Limestone and dolomite, which are often formed as the shell remains of animals, are usually treated as true minerals.

Fact #28 Minerals will often form crystals , a three-dimensional body formed by the regular and repeated arrangement of the atoms found in that particular mineral.

Fact #29 When a force is exerted on many crystals, the crystals will break into a predictable pattern, called a cleavage or cleavage plane .   These is because some of the atoms in the crystal hold onto other atoms more tightly (called bonding).   Breaks will occur between the atoms that are more weakly bonded together.   Many minerals can be identified due to the unique angles that are created when the mineral (crystal) is broken.

Fact #30 Hardness is a property of minerals that compare the bonding forces of the atoms between two different minerals.   A standard of minerals exists, called Mohs Hardness scale.  

Talc (hardness of 1) is the weakest mineral and diamond (rated a 10) is the hardest.

Fact #31 The mineral feldspar (German: "field stone") is a major component of granite.   There are two basic types: 1) Plagioclase feldspar has sodium and calcium atoms mixed in with the main matrix of aluminum, silicon and oxygen atoms. 2) Alkali feldspar has the potassium atom replacing the sodium and calcium atoms.

Fact #32 Minnesota Stone

•  Minnesota ranks seventh in the nation in total value of production of dimension stone products from granite, limestone, and quartzite.
•  The Iron Range, Cold Spring, and the Minnesota River Valley have had clusters of mines since early statehood.
•  Minnesota stone is primarily classified into two broad categories of uses: building (dimensional) stone, and construction aggregates.
•  Iron ore bedrock is mined on the Mesabi Iron Range at the rate of more than 100 million tons per year.
•  Minnesota produces 2/3 of the U.S. production of iron ore.
•  Some of the by-products of iron ore production include construction aggregates and landscape stone.
•  Stromatolite from the Mesabi Iron Range features two-billion year old multi-colored fossilized algae.
•  Minnesota is home to some of the oldest rock formations in the world. Morton Gneiss (guh-nice), a granite,   is one of the oldest rocks that have ever been dated and is the oldest stone in widespread use as a decorative building material. Minnesota granite-gneiss has been dated by the U.S. Geological Survey as 3.5 billion years old.
•  Red limestone, mined near Shakopee, is used for landscape stone and baseball diamond infields.

A short list of buildings and monuments that use Minnesota stone includes:

• Memorials in Washington, D.C.: The Korean War Memorial; the Second Division Memorial (granite from Cold Spring Granite Company)
• Mount Rushmore Walk of Flag Columns and Visitors Center Pergola (granite from Cold Spring Granite Company
• National Museum of the American Indian, Washington, D.C. (dolomite from Vetter Stone Company and Pipestone)
• Philadelphia Museum of Art, Philadelphia, PA (dolomite from Mankato-Kasota)
• U.S. Capitol, Washington, D.C. (East front center step - granite from Rockville, Minnesota)
• Museum of History and Technology, Smithsonian Institution, Washington, D.C. (curbs and fountain steps, Minnesota pearl pink granite)
• Two Fountains at the Eclipse at Constitution Ave NW, Washington DC (Each is carved from a single block of Morton gneiss.)
• Museum of American History, Smithsonian Institution, Washington, D.C. (granite steps and trim)