Analytical Methods:Field Carbonate Determination

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Calcium carbonate determination
based on the method of the Soil Survey of England and Wales ([Hodgson, 1976>Main.Glossary.Reference.Hodgson1976])

Questions
On-site confirmation of calcium carbonate in soils, sediments and artefacts. This technique can be used to:
 * Determine whether areas colour differences (greyness) reflect different depositional contexts or whether they have been affected by post-depositional calcium carbonate formation.
 * Identify the presence of limestone and other calcareous stones in soils and sediments.
 * Identify deposits where shell and bone preservation should be good (should be used in combination with soil pH).

Required equipment and chemicals1
Make the acid by mixing 1 part concentrated HCl1 (37%) with 11 parts distilled water. Always add the acid to the water and not the other way round.
 * 1M HCl (1 molar Hydrochloric acid)
 * Dropping dispensing bottle

Method
Take a small sample (ca. 1 g) of the deposit and apply a drop or two of acid. Watch and listen (hold close to the ear) for a reaction as bubbles of carbon dioxide gas are produced (effervescence). Alternatively the acid can be applied to a particular soil feature or coating of interest.

Data and interpretation
This is a semi-quantitative analysis in soils or sediment containing up to 10% calcium carbonate. The percentage content cannot be further quantified above 10%.

Dolomite (Calcium magnesium carbonate) reacts only weakly with 1M HCl, but will visibly react with 6M HCl1 (1 part concentrated HCl to one part distilled water). However, the reaction cannot be quantified as for calcium carbonate.

Safety
1 Always consult chemical safety data sheets and follow appropriate health and safety protocols before handling or using chemicals.

Many chemical safety data sheets are available here from this Oxford University based database.

Related Techniques

 * Field soil pH
 * Laboratory soil pH

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