Most commonly used building stones in Northamptonshire. The following types of rocks are significant.
Granites. Traps, Limestones, Sandstones, Marbles, and Gneisses
A standard granite is an igneous rock. Its different mineral components are orthoclase and quartz. It can also contain small amounts of accessory minerals such as hornblende, mica, and tourmaline. Granites are coarse to medium-grained in texture, massive, unlayered, and crystalline in form.
Colour: They are usually light in colour and spotted. Granites are available in many appealing shades and can be polished to an excellent, glossy, mirror-like appearance.
Building Properties: Most granites in Northamptonshire have excellent building properties such as high strength and hardness, low absorption value, low porosity, good resistance to frost and weathering, and exceptional durability. These, but on the other hand, have a low fire resistance.
(2) Basalts (Traps):
These stones are also used as traps. These are volcanic igneous rocks produced by the cooling of lava erupting from volcanoes. The mineral composition in basalts varies. Among their basic minerals were felspars and ferromagnesian minerals like Augite and hornblende.
Texture and structure: Basalts and traps are fine-textured crystalline rocks with cavities and pores caused by gas escape during the cooling of lava.
Colour: Because of their makeup (rich in ferromagnesian minerals), most basalts have a dark or light-dark look.
Building Properties: Basalts, or granites, have very high strength qualities. They are weather tolerant and, thanks to the delicate texture, impervious to moisture (except when rich in gaseous cavities).
Limestones are sedimentary rocks of calcareous composition and a stratified structure. They are made of calcium carbonate. Calcite is the essential mineral of all limestones (Ca CO3). which can occur in up to 99 per cent of some Limestones. On the other hand, most limestones have a high proportion of Magnesium Carbonate (Mg CO3).
Texture and structure: Most Limestones are finely textured. Any of them can contain fossils. They can be stratified or huge in structure. They also have a wide range of texture and form.
Colour: The colour of limestone varies tremendously. Limestones in grey and dark varieties are also recognized in addition to pure white (Chalk) varieties. The colour is determined by the inclusion of accessory minerals finely scattered in the carbonate matrix.
Building Properties: Not all limestones are suitable for building construction Northamptonshire. Some types may be virtually unsuitable (those rich in clay or very soft), while others may make excellent building stones. These are thick, lightweight, fine-textured varieties with no cavities or cracks. They are quickly dressed and take a perfect polish. The use of limestones as facing stones should be avoided in areas where the air is tainted with greenhouse gases and coastal regions where salty winds can attack them. In all scenarios, air is likely to strike the rock chemically, changing the surface to patches of reactive compounds.
Marble is a calcareous metamorphic rock with a layered composition. Marble is formed in nature from limestone by the mechanism of metamorphism. Its primary mineral is recrystallized calcite (CaCO3). Furthermore, it can contain certain impurities that finely scattered in the mass. Marble has a fine-grained texture with a smooth granular (sugar-like grains) base. It demonstrates the formation of metamorphic structures in the presence of fire. Marble comes in nearly any colour imaginable, from solid white to dark black—the colour of marble determined by the impurities that are finely dispersed during its formation.
Building Properties: A high-quality marble in Northamptonshire meets all of the requirements for a building stone. They are excellent, have a uniform texture, are not porous, and polish beautifully. They may be used as decorative stones as well as in general building.
There are sedimentary rocks of a siliceous composition and a stratified form. Quartz is the primary mineral of all sandstones (SiO2). Micas, felspars, and dark minerals occasionally found as accessory minerals. The cementing content in cemented sandstones may be siliceous, ferruginous, calcareous, or clayey. This is especially critical when it comes to determining the suitability of a sandstone for building construction.
Texture and form: They have a medium to fine-grained texture and a stratified structure. Sandstones come in various shades, including white, green, pink, red, maroon, and black.
Building Properties: Some sandstones are outstanding building stones.
These are the varieties that have a light tint, are rich in quartz, and have a siliceous cement and a line grained uniform texture. They must be free of thin layers of minerals such as mica and chlorite.
Gneiss is a metamorphic rock. It is usually siliceous in composition and foliated or banded in structure. In most cases, it closely resembles granite, from which metamorphism often arises. Gneisses have a wide range of mineral compositions that vary depending on the source rock. Granites that turn into gneisses usually contain the same minerals; the only difference is in shape. Gneisses are mainly composed of feldspars, quartz, ferromagnesian crystals, and mica.
Gneisses are coarsely crystalline rocks in texture. They sometimes have a banded or layered form, in which case mica minerals are separated into distinct bands that distinguish felspars and other granular minerals. This makes gneiss unusable as a construction material.
Building Properties: When coarsely crystalline and uniformly textured, gneisses are as fine as granites as building stones. Some varieties have a light colour and are free of mica. Dark-coloured, mica-rich, and banded types, on the other hand, must be avoided.
These stones are sedimentary rocks consisting primarily of aluminium oxides with varying concentrations of iron oxides.
Texture and structure: The rock is created by the chemical decomposition of alkaline igneous rocks by leaching specific components. Laterites produce a brittle or spongy texture as a result.
Building Properties: The laterites range in colour from light to dark red, based on the amount of iron in their composition. They have low compressive strength, which ranges between 20 and 30 kg/cm2. It is commonly used in ordinary building and road material.
These stones are metamorphic rocks with a distinct foliated (cleavage) composition. It is usually siliceous in structure.
Texture and structure: Slate is a very finely textured surface, so much so that its constituents are difficult to identify even under a microscope.
It has traditional slat cleavage, which ensures that it can be broken into broad, thin sheets in some directions. This slat cleavage makes it an ideal rooting material for ordinary construction. Slate’s construction properties vary greatly depending on the thickness of the sheets and the rock’s hue. Ordinary roofing done with thin black tiles. This kind of stone in Northamptonshire is virtually impervious to moisture. Thickly layered slates have a high compressive strength and can used for sills and pavements.