Portland Stone - Inmosthay Quarry
Click the microscope button to view a thin section for this sample.
Click the microscope button to view a thin section for this sample.

Fact sheet

Portland Stone - Inmosthay Quarry

This oolitic limestone rock was deposited in a warm shallow sea not far from land during the Jurassic period around 140 million years ago. The sample comes from a large quarry in the centre of the Isle of Portland in Dorset. Portland stone has been used as a building stone since Roman times and was used in the construction of Buckingham Palace and St Paul's cathedral.

The thin section shows that the rock is dominated by spherical ooids with cores of shell fragments and angular quartz grains coated by carbonate micrite cement in concentric layers. The rock also contains shell fragments, including mainly fragments of bivalves. Some of the pore spaces between shell fragments and ooids remain open but the majority are cemented by micrite and sparry calcite. The almost complete filling of pore spaces in this limestone by cemented micrite (carbonate rich mud) and sparry calcite has made it more resistant to erosion and thus a good building stone.

Additional images
  • limestone - width 2.5 cm
  • limestone - width 6 cm
  • limestone - width 12 cm
  • limestone - width 12 cm
50.5523, -2.4418
Inmosthay Quarry, Isle of Portland, Dorset
About this collection

The United Kingdom Virtual Microscope (UKVM) collection consists of igneous, sedimentary and metamorphic rocks from around the UK.

It is intended as a teaching resource, helping to tell the story of the common rock types and how they form, and reflecting the history of the UK at the margins of the continent of Europe. The collection is a series of teaching sets, for example igneous rocks from the North Atlantic Igneous Province and SW England; high-temperature metamorphic rocks from Scotland and low-temperature metamorphic rocks from Wales; and sedimentary rocks, including English limestones and sandstones.

Sample details

Rock-forming mineral
Category guide  
Category Guide
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow users to search for broad terms like ‘granite’ as well as more specific names such as ‘breccia’. However, the adjacent descriptions of the specimens captures a wider range of general words and phrases and is a more powerful search tool.
Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Selecting one or more period, for example 'Jurassic'.
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
The owner of the sample that appears in the collection. For example, NASA owns all the samples that appear in the Moon Rocks collection
We would like to thank the following for the use of this sample: