Limestone is an unusual rock in that it fizzes when dilute acid is placed on its surface. It is the presence of calcium carbonate that is responsible for this. The calcium carbonate content of limestone rocks has been used from the earliest civilisations, dating back to 14,000 BCE, to its extensive use in modern times.
Limestone is a rock that dominates the landscape in many areas of New Zealand and is literally ‘fizzing’ with uses and applications, so it deserves closer inspection that will reveal some interesting chemistry, geology and biology.
Limestone is a very common sedimentary rock composed mostly of the mineral calcite. Most limestones have a marine origin, being formed by the accumulation of shells and shell fragments of once-living marine organisms such as molluscs, bryozoans and corals. Other limestones, such as cold-seep carbonates, have been derived from non-biogenic mineral formation as a result of direct crystallisation of calcium carbonate from water. Find out more in the articles Limestone origins and New Zealand limestone origins.
If most limestones have a biogenic origin, it may be of value to discover how marine organisms like bryozoans and molluscs extract calcium carbonate from seawater and lay it down in crystalline form to form a hard protective outer casing or shell. By understanding the biological and chemical principles that are at work, these natural processes may be able to be reproduced in the lab to develop a new generation of materials for everyday use. Find out more in the article Calcium carbonate biomineralisation.
Limestone contains more than 50% calcium carbonate in the form of the minerals calcite and aragonite. High-grade limestone can be close to 100% calcium carbonate. Calcium carbonate has a wide range of uses, and a study of its physical and chemical properties will help to explain why it has so many applications. Find out more in the article Carbonate chemistry.
Lime – a ‘top 10’ chemical
The term ‘lime’ is used for several calcium compounds. Pure lime is calcium oxide, which is produced industrially by the thermal decomposition of limestone. As a ‘top 10’ chemical in terms of worldwide production, lime plays a key role in a multitude of industrial, manufacturing and agricultural processes. Find out more in the article Lime – a time-tested chemical.
Limestone is quarried for aggregate and building stone for use in road and building construction, as well as being used for making agricultural fertiliser, cement, steel and glass. High-purity limestone is used as a mineral filler in paper, paint, plastics, rubber and carpet backings as well as in water treatment and as a dusting agent in coal mining to prevent fires. Find out more in the article Limestone uses.
Limestone is a sedimentary rock that is partially soluble, especially in rainwater, which is naturally acidic, and therefore forms many erosional landforms. It dominates the landscape in many areas of New Zealand such as the Waitomo region of Waikato, Te Mata Peak in Hawke’s Bay, the Matiri Range in Nelson and Punakaiki in central West Coast. These landscapes have considerable tourism value. Find out more in the article Limestone landscapes.
Meet the scientists
Professor Kathryn McGrath is director of the MacDiarmid Institute for Advanced Materials and Nanotechnology. One of her research interests focuses on calcium carbonate biomineralisation. The long-term goal of this work is to apply the mechanisms of biomineralisation to develop human bone replacement materials that can be used in the medical setting.
Professor Cam Nelson from the Earth Sciences Department at the University of Waikato is regarded as one of New Zealand’s limestone experts. His research work in this area has spanned a lifetime and has led to a clearer understanding of limestone formation in temperate marine environments.
Dr Steve Hood works closely with Professor Nelson, and one of his research interests focuses on cold-seep carbonates, both modern and ancient.
Often associated with cold-seep sites is a vibrant community of chemosynthetic organisms. Dr Ashley Rowden from NIWA specialises in the identification of these unique living forms.
Take up the challenge
The related student activities are a combination of worksheet-based, practical and art experiences.
Limestone to lime uses the interactive Calcination (the industrial processing of limestone into lime) to complete a matching activity. Toilet roll geological timescale uses a toilet roll to mark major New Zealand gelogical events. In Discovering limestone's secrets, students answer graded sets of questions based on the interactive Limestone secrets revealed.
Art enthusiasts can prepare a tile of lime plaster, paint it in the fresco style and learn about Fresco painting chemistry.
For explanations of key concepts, see Limestone, a fizzy rock – key terms.