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This earthcache is located close to the roadside. Parking is on the verge. Please pull off the road. Spilsby sandstone takes its name from the market town located about 5 miles away.
Sandstone
Sandstone is a type of sedimentary rock. It is made up of particles of pre-existing rocks and minerals. These particles are usually igneous rocks, metamorphic rocks or even other sedimentary rocks.
Sandstones are originally clastic. They are generally found under seabed, riverbed, or under desert areas. Under the influence of some type of current (wind, waves, flowing water, or glacier) the layer of particles starts depositing one above another. They are composed of fragments or particles of older rocks or previously existing solid matter. The cement binding these grains is especially silica, calcites and clays.
Formation
The formation of sandstone involves two primary stages. At first, due to sedimentation, a layer or layers of sand accumulate either from air (in deserts) or from water (in rivers, lakes, sea). Sedimentation occurs by settling of sand grains down the bottom of seabed, riverbed or, on the ground surfaces. This process of sedimentation continues to hundreds or thousands of years. Gradually thick layers of sand deposits one above another. Slowly and steadily, the upper layers exert pressure on lower layers. Other external agencies, like water (in river, sea) and air, also exert pressure on these layers. Due to these external effects and pressure of overlying deposits, the sand consolidates and changes in sandstone. It is cemented by the precipitation of minerals within the pore spaces between sand grains. Silica and calcium carbonate are the common cementing materials.
Classification Based on Grain Size
The sand grain size covers the range 0.1 mm to 2 mm.
• Argillaceous: The rocks with smaller grain size include shales, clays and siltstone and are typically called Argillaceous sediments.
• Rudaceous: The rocks with larger grain size include Breccias and conglomerates and are known as Rudaceous sediments.
The characteristics of the resulting sandstone, like grain size, colour, sedimentary structures etc. is largely determined by the environment where it is deposited.
Physical Properties of sandstone
• Colour-Different varieties of colours are available like red, yellow, white, pink, gray and many more.
• Hardness- On moh's scale its density lies between 6 and 7.
• Comprehensive strength-It is usually between 360 to 465 kg/m2 u
• Porosity-Usually porosity is very low.
• Density-2.30 to 2.41 kg/m3
• Water absorption-The water absorbing capacity is up to 1% only.
Chemical properties of sandstones:
The chemical constituent of sandstone is same as sand. It is mainly made of quartz. The cementing constituent that binds it together is usually silica, calcium carbonate, and iron oxide. Sandstones are vastly resistant to alkali, acids, and heat.
Spilsby Sandstone
Spilsby sandstone is a variant of the above. It was widely used in the building of local churches, resulting in their distinctive ‘green’ colour. A good example can be found at St James parish church, Spilsby which is about 5 miles from this site.
The following is a lithological description of Spilsby Sandstone provided by The BGS Lexicon of Named Rock Units.
“The Formation comprises two members that are further divided:
Upper Spilsby Sandstone Member. Thin, coarse-grained, grey or brown pebble sandstone with iron oolites. Underlain by fine-to medium-grained, buff, yellow and white sands with sparse calcareous "doggers".The latter sands become coarser and greener towards the base of the Member. A bed of phosphatic nodules and small [generally chert] pebbles occurs at the base,
Lower Spilsby Sandstone Member. Coarse-grained, pebbly, glauconitic sands and sandstones with calcareous "doggers" and sporadic phosphatic nodules towards the Top. The base of the Member comprises a thin grey sandstone with phosphatic nodules. “
To complete this Earthcache, please email me with the following information:
1. Using the Geochronostratigraphy division of time, between which age ranges does Spilsby Sandstone lie?
2. Which mineral gives Spilsby sandstone its distinctive green colour?
3. Estimate the height of the outcrop of Spilsby sandstone at the given co-ordinates.
Optional activity: Take a picture of yourself and/or your GPS unit beside any of the stone types mentioned above. Attach this to your post.
Answers must be emailed to me in order to claim the cache, and an optional photo may be uploaded as suggested above. Logged finds with incorrect or incomplete answers may be deleted.
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