ROCKS AND
ROCK IDENTIFICATION

---

Rock identification is not the specialty of Don or the Vagabonds, but we join others with the insatiable urge to figure out what a rock is when we find an interesting one. In that regard, we provide notes,  references and links to useful resources that we use in rock identification. 

With limited or no knowledge of rocks and their identification, you might want to start by reading about rock identification, specifically, “How to  look at a Rock” by Andrew Alden at http://geology.about.com/od/rocks/tp/rocks101.htm. This site has been around since at least 1997 and as a result is a wealth of information.  

Real rock identification is an exercise in observation, testing and flawless logic. 
         ·  Observation is basically just looking at the rock and identifying  what color it is; how it’s made - the size of the crystals that make up the  rock, whether or not you can see layers or minerals in the rock, and the grain  sizes within the rock (this might require a magnifying glass). 
         ·   Testing involves simply seeing if it reacts to a magnet; and/or scraping the rock with a fingernail, a coin, a nail and/or handtool; and/or  dropping diluted acid  (a pool chemical) on the rock and seeing how it reacts; and/or scraping the rock on a prepared surface and seeing what  color streak is left behind

Hardness test scale. If you can scratch the rock with your fingernail, then hardness is 2.5 or less; if you can scratch a knife blade with a point of the rock, then hardness is 7.0 or less. Very useful test for identifying a rock.

---

A simple test kit
This is only an example, many kits are available.
https://www.usgeologicalsupply.com/mineral-test-kit.html​ or ​https://cornerstone-edsupply.com/products/geology-testing-kit

---

         ·   Flawless logic is the art of using a decision tree to decide rock attributes in an organized way that leads to the identification of a rock.  Here’s a basic one that does a good job for  beginners:

http://dickasonscience.com/mr%20dickason/rock%20Cycle.html

---

Another good starter decision tree from the web that has slightly different questions is this  one…

http://pmt-5th-grade-science.wikispaces.com/Rock+Identification+Key  ; (S) = sedimentary rock, (I) = igneous rock, (M) = metamorphic rock

---

The rockhounds website below offers an  interactive decision tree on the web and is very useful.
http://www.rockhounds.com/rockshop/rockkey/

For a more sophisticated decision tree, see Art Crossman’s excel table at
                http://geology.com/minerals/mineral-identification.shtml
It's a four page excel spreadsheet with part of the first page that looks like this...

http://geology.com/minerals/mineral-identification.shtml

---

Rocky has cataloged 10 different decision trees/websites on rock identification and has found that collectively they identify 94 different rocks. However, no one chart ever identifies more than 42 rocks and most identify 12-20 in one chart. So if you're using a decision chart and you're having trouble getting your rock to fit, be aware that there are many more rock possibilities out there and you may need to move to another, usually more complex, chart to finalize your identification. 

Additional information/references are noted  below: (information below is currently being edited...)

    Books
            "The Practical Geologist" by Dixon/Bernor


    Pamphlets
            “A Field Guide to the Identification of PEBBLES” by Eileen Van der Flier-Keller

 
     On the web
             http://www.rockhounds.com/rockshop/rockkey/ 
 
             http://geology.about.com/od/rocks/a/Rock-Tables.htm 
 
             http://geology.about.com/library/bl/images/blimageindex.htm (glossary of geologic terms)

            http://geology.about.com/od/rocks/a/Rock-Picture-Index.htm (index of 71 rock pictures)


Hope the above helps and gets you started.   If you have a great rock please let us see it!

                                    Don’t forget,“GEOLOGY ROCKS!”…the Vagabonds.