CALCITE ROCK

Product Description

Calcite (calcium carbonate, CaCO₃) is one of the most common and instructive minerals in any teaching collection because it reacts so visibly with dilute acid. A drop of dilute hydrochloric acid on this specimen produces a distinct fizz of carbon dioxide bubbles — the standard classroom test used to separate carbonate minerals like calcite from silicates and other mineral groups. Students can also observe calcite’s rhombohedral cleavage, where broken fragments consistently split along smooth, slanted faces rather than fracturing randomly.

As the primary mineral in limestone and marble, calcite ties directly into lessons on sedimentary and metamorphic rock formation, cave systems, and the carbon cycle. Its relatively low hardness (around 3 on the Mohs scale) also makes it a useful reference point when teaching students to rank minerals by hardness using a simple scratch test.

Specimen Details

Classroom & Lab Applications

• Acid-fizz test demonstrations for carbonate mineral identification
• Cleavage observation exercises using rhombohedral fracture patterns
• Lessons on limestone, marble and the rock cycle
• Introductory carbon cycle and cave-formation (karst) discussions

Care & Handling

Use only small, dilute acid quantities for fizz testing, applied with a dropper on a disposable surface, and follow standard school lab safety practice for acid handling. Rinse and dry the specimen after any acid test to prevent surface etching, and store it separately from harder minerals that could scratch its relatively soft surface.

Why Choose LabEquip

This Calcite Rock specimen is part of LabEquip’s Educational Rock and Minerals range for hands-on earth-science teaching. It pairs naturally with our mineral streak identification collection for a complete identification workflow, and with basic reagents from our Chemistry Lab Equipment range for acid-test demonstrations.

Frequently Asked Questions

1. Why does calcite fizz when acid is applied?

Calcite is calcium carbonate, which reacts with acid to release carbon dioxide gas as visible bubbles. This effervescence test is the standard way to distinguish carbonate minerals from other mineral groups in the classroom.

2. How hard is calcite on the Mohs scale?

Calcite sits at about 3 on the Mohs hardness scale, meaning it can be scratched with a steel nail or knife blade but not with a fingernail alone, making it a useful mid-range reference mineral.

3. What is calcite’s cleavage pattern?

Calcite shows perfect rhombohedral cleavage, splitting along three directions to form slanted, parallelogram-shaped faces rather than breaking with a random fracture.

4. How is calcite related to limestone and marble?

Calcite is the dominant mineral in both limestone, a sedimentary rock, and marble, the metamorphic rock formed when limestone is subjected to heat and pressure, making it a useful bridge specimen between sedimentary and metamorphic geology lessons.

5. Is this specimen suitable for acid-test demonstrations in school labs?

Yes, it is commonly used for dilute acid-fizz demonstrations. Schools should follow their own lab safety protocols for acid handling and use only small, controlled quantities.

6. How should this specimen be stored between classes?

Keep it dry, rinse off any acid residue after testing, and store it in a labelled tray away from harder minerals that could scratch its relatively soft surface.

Last Updated: September 2026