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Pegmatite ("PEG-mah-tight") 

Pegmatite is a rare find in our area.  We've seen pegmatite boulders outside of a few buildings, and we can buy bags of crushed pegmatite from only a few local suppliers.

To learn more about pegmatite, scroll farther down this page.
  

Crushed pegmatite rock

  

bulletHow to recognize pegmatite
bulletOther rocks that look like pegmatite
bulletSpecial things to look for
bulletWhere pegmatite came from
bulletHow pegmatite formed
bulletOther names for pegmatite
bulletLinks to Web sites about pegmatite
  

How to recognize pegmatite

bulletLarge pieces of pegmatite are usually a mix of colors:  Pink, white or cream, silvery, and sometimes darker colors.  Smaller, broken-off crystals may be only one color.
bulletPegmatite crystals are usually pretty big:  peas-sized or larger.
bulletYou cannot scratch most pieces of pegmatite with a nail or knife.  (See more about the scratch test.)  Only silvery mica crystals can be scratched with a nail or knife.
bulletPegmatite is made mostly of the minerals feldspar and quartz.  Pink, white, or cream-colored feldspars break to form flat surfaces.  Quartz crystals may be a semi-clear or grayish, and they break to form curved, glassy surfaces.
bulletOther common minerals are mica (which breaks to form flat silvery sheets) and dark iron-magnesium minerals, like hornblende and augite.
    

Other rocks that look like pegmatite

Red granite:  
bulletLike pegmatite, red granite is also pink or reddish in color and is made of several kinds of minerals, most of them hard to scratch.  
bulletHowever, granite crystals are smaller than pegmatite crystals (usually pea-sized or smaller).
    
Saprolite:  
bulletSaprolite is also reddish in color, and freshly broken surfaces may be hard to scratch.
bulletSaprolite is weathered granite, so most crystals will be smaller than a pea.
  
Pink quartzite:  
bulletPink quartzite is also reddish in color and hard to scratch.
bulletHowever, pink quartzite is made of just one mineral (sand-sized quartz grains).  There are no flat-faced broken feldspar crystals, grayish quartz crystals, or crystals of mica or darker minerals.
   

  
Where pegmatite came from

Pegmatite is fairly common in the Rocky Mountains
of Colorado.  "Royal Gorge" is the trade name for the
pegmatite boulders and landscape stone sold in our area.  
Royal Gorge is also a canyon that cuts through the Front 
Range of the Rockies, near Canon City, Colorado.  

So, we're wondering, is that just a coincidence, or was our 
pegmatite quarried in that part of Colorado?

  

How pegmatite formed

Pegmatite formed as melted rock cooled slowly, far 
below the surface of the Earth.

  

Other names for pegmatite

We use the scientific name "pegmatite" for this rock,
but it is also known by other names:

bulletWe've seen 50-pound bags of pegmatite gravel labeled "Royal Gorge."

 

Here are some ways to classify pegmatite (by grouping it with similar types of rocks):
 
bulletPegmatite is an igneous rock, because it formed as melted rock cooled and hardened.
 
bulletPegmatite is sometimes classified as an intrusive igneous rock, because the melted rock cooled slowly, deep inside the Earth.

   

Links to Web sites about pegmatite

The Pegmatite Zone defines and describes pegmatite, and 
shows photos of some beautiful minerals found in pegmatite 
rocks.
   < http://www.gemandmineral.com/peg.html >

    


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Copyright 2001-2002 Eric D. Gyllenhaal                                           Search this Site
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This page was created on May 2, 2001, and it was last updated on July 27, 2002.