Acid Test for Rocks
If a sedimentary rock is made largely of the mineral calcite, it might be an
organic sedimentary rock formed from once-living organisms. In this activity, you will test for calcite in two sedimentary rock samples.
INQUIRY FOCUS Draw Conclusions
Procedure
1.
2.
Obtain a sample of ordinary limestone
and a sample of coquina. Use the hand lens to
observe the color and texture of each sample.
Record your observations in the table below.
Next, obtain a small amount of dilute
hydrochloric acid from your teacher. Hydrochloric
acid is used to test rocks for the presence of the
mineral calcite. Use the dropper to place two
drops of hydrochloric acid on the sample of
ordinary limestone. Record your observations in
the table below.
Ordinary limestone
Materials
plastic gloves
two rock samples:
ordinary limestone,
coquina
hand lens
dilute hydrochloric acid
plastic dropper
running water from a tap
Coquina
Color
Texture
Reaction to Acid
3. Repeat Step 2 with the coquina sample.
4. Rinse the rock samples with water before returning them to your teacher.
Then wash your hands.
Think It Over
What conclusion can you draw about the mineral composition of ordinary
limestone and coquina?
What are the independent and dependent variables in this activity?
SEDIMENTARY ROCKS