Identification of Sedimentary Rocks

Tools You Need

You need only two  things to start identifying sedimentary rocks:  A magnifying glass, and a small amount of DILUTED Hydrochloric Acid (HCL) in a 2-ounce plastic squeeze bottle or dropper bottle (with screw cap).  A used squeeze-type medicine, eye drop, or lens solution bottle will work, but be SURE to deface the label and write "ACID" and "POISON" on your bottle in big letters!!

To make a weak acid solution for testing rocks, ASK AN ADULT to add one (1) part concentrated HCL (Hydrochloric Acid) to nine (9) parts water.  For instance, 1 ounce of acid is added to 9 ounces of water, or 10 drops of acid is added to 90 drops of water.  If there is no HCL available, Muriatic Acid (used for swimming pools) should work.

ALWAYS ADD ACID TO WATER, NOT THE OTHER WAY AROUND! WEAR EYE PROTECTION!

ALWAYS ADD ACID TO WATER, NOT THE OTHER WAY AROUND! WEAR EYE PROTECTION!

Why is acid always added to water instead of water being added to acid?  When acid and water are mixed, a large amount of heat is generated.  Adding acid to water minimizes the heat that is produced.  Adding water to acid may result in a dangerous explosive-type boiling of the solution, splashing the stuff everywhere.  SINCE ACID CAN SEVERELY DAMAGE YOUR EYES AND SKIN, ALWAYS ADD ACID TO WATER, NOT THE OTHER WAY AROUND! 

WEAR GOGGLES AND PROTECTIVE CLOTHING!  DO NOT SPLASH ACID IN EYES OR ON SKIN!  IF ACID GETS IN EYES OR ON SKIN, FLUSH UNDER COLD RUNNING WATER FOR AT LEAST 15 MINUTES! GET MEDICAL HELP!  Concentrated acid is dangerous, so be careful.  After it is diluted, it's not so dangerous, but still avoid getting it in your eyes, on your skin, or on your clothes.

Fill up your squeeze bottle or dropper bottle and store the extra diluted acid in a glass bottle or jar.  Mark the extra bottle or jar clearly: "HCL ACID - POISON" and store it in a cool, dry place.

How To Test a Rock

Start by placing a few drops of DILUTED HCL on your rock sample.  Look closely for bubbles.  If you see bubbles, use the lower part of the chart to identify your rock sample.  If you don't see bubbles, use the top part of the chart.

Here are pictures of some common sedimentary rocks:

Don't worry about color when you identify your rocks.  Sedimentary rocks can be almost any color!  Use the chart above instead!

 The Chart entitled "Key to the Identification of Basic Sedimentary Rocks" is courtesy of

Lynn S. Fichter
Department of Geology and Environmental Science
James Madison University, Harrisonburg, Virginia 22807