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Slate 

In our neighborhood, we've found a few gardens with slate gravel or stepping stones -- and a few churches have roofs made of slate.

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

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

How to recognize slate

bulletThis slate is mostly gray in color.  (There are also reddish, maroon, and greenish varieties of slate.)
bulletSlate looks silky in the sun.  (Shale looks dull in the sun.)
bulletSlate usually breaks into flat pieces.
bulletYou can scratch slate into light gray powder with a nail or knife.  (See more about the scratch test.)
bulletSlate grains are usually too small to see.  Slate made mostly of tiny grains of quartz, mica, and other minerals.  Sometimes slate also contains larger crystals, like garnets.
    

Other rocks that look like slate

Obsidian:  
bulletBreaks into, blocky chunks with sharp edges.
bulletLooks glassy, not silky.
bulletA nail usually doesn't scratch it.
  

Special things to look for

Look for:
bulletSlate's silky shine in the sun
bulletWavy patterns on some pieces 
bulletLittle lumps made by crystals of garnet embedded in some slate
  
Look for white streaks called "veins."  They are made of calcite, quartz, and other minerals.  (Calcite can be scratched by a nail and it bubbles when you put vinegar on it.  Quartz can't be scratched and it doesn't bubble.)
  
Look for pieces where the slate's layers have been bent or folded.
  

  

Where slate came from

We know that the slate we find was dig out of the 
ground or "quarried" somewhere else and then 
shipped to our area.  However, we're not sure where 
it was quarried.  We've read about slate quarries in 
Pennsylvania, Vermont, New York, Maine, and 
Maryland, so it may have come from one of those 
states.
  

How slate formed

Slate was originally another kind of flat rock, called shale.

Shale is made of tiny grains of clay and other minerals
cemented into rock.  When shale is buried deeply and 
exposed to great heat and pressure, the clay changes 
into new minerals (like shiny mica) and the shale becomes 
slate.
  

Other names for slate

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

bulletWe've seen 50-pound bags of slate gravel labeled "gray slate."
bulletLarger piece of slate are sometimes called "flagstone"

 

Here are some ways to classify slate (by grouping it with similar types of rocks):
  
bulletSlate is a metamorphic rock, because it was changed by heat and pressure from one rock type into another.
  
bulletSlate is sometimes classified as a meta-sedimentary rock, because it was originally a sedimentary rock.

   

Links to Web sites about slate

Here's a Web page about slate quarrying in Wales.
   < http://www.penmorfa.com/Slate/ >

The American Slate Company has a Web page called
"A Short History of Slate."
   < http://www.americanslate.com/HistoryPage.html >

The Echeguren Slate Company imports slate from
all over the world.
   < http://www.echeguren.com/ >

  


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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.