Rocks which have grains

These may be fragments of crystal or whole crystals and they can be mm to cm in size. A 'rock' may have only one type of mineral, but usually it consists of several different minerals. So how do you know whether you're looking at a rock or a mineral? A rock is an aggregate of one or more types of minerals which may be present as crystals or grains. If your specimen is a single or collection of crystals, all made up of the same thing, you're probably looking at some kind of mineral.

If it's metal, you could be in luck, it might be a native element like gold or silver, or more likely, it's one of the sulphide minerals like pyrite - often known as fool's gold. Alternatively, there's a very small outside chance it's part of a meteorite! In which case you should send it with details of when and where you found it to either the Natural History Museum or to the Open University, and get us to identify it for you. Don't worry, we'll send it back!

If you're fairly sure you're looking at a rock, before you try to work out its mineral composition, you should first look at its texture.

Texture Texture is the term used to describe the physical relationships between the particles from which the rock is made. Virtually all rocks have textures that are either crystalline made of crystals or fragmental made of grains.

In rocks with a crystalline texture, the minerals have grown together as interlocking crystals. In rocks with a fragmental or granular texture, individual mineral and rock grains have been transported and deposited, and may be quite rounded. In either case the size of the individual grains can vary considerably. Rocks with crystalline texture are usually harder and more compact than those with granular texture. When crystalline rocks are broken they tend to fracture along smooth, angular surfaces within individual crystals, rather than between crystals.

The result is that the broken surfaces of crystalline rocks have lots of flat faces that reflect and glint as they catch the light. Rocks with granular texture usually fracture between individual grains because the 'cement' holding them together is often weaker than the grains themselves.

Layering After texture, grain size and colour, you should consider if there are any 'structures' in your rock. By 'structure' we mean are there any bands, sheets or layers? Layers can be bands of different coloured crystals, different sizes of grains, or the rock may simply split into thin sheets, like slate. Ribbon-like layers of crystals ; Grain size layers or Thin plate-like layers or sheets. Ribbon-like layers of crystals: In some rocks different coloured minerals are lined up in ribbons.

Usually in two colours, black and white, or green and white, or black and pink. Ribbon-like layers are often typical of metamorphic rocks where the minerals grow in layers in response to pressure. Grain size layers: In sedimentary rocks, grains of different sizes are deposited as the strength of the current waxes and wanes gets stronger or weaker. Larger grains are deposited by stronger currents. Smaller grains are deposited by weaker currents. Often when grains are sorted by wind or water, they will be the same composition and shape, but different sizes; and therefore different shades of the same colour.

Thin plate-like layers or sheets: Some minerals grow naturally to form platy sheets - but it takes added temperature and pressure to bring them all into line so that they form sheets or layers.

Clay minerals are typically flat and platy, but if they undergo metamorphism they will line up into sheets and form a rock which easily splits - like slate. For example: mudstone contains lots of flat platy clay minerals - but it doesn't easily split into layers because the minerals are arranged in a random pattern.

However, if you add heat and pressure all the clay minerals will align themselves so they are roughly parallel to each other and the rock will split very easily giving you "slate". Fossils What are fossils? The word fossil comes from the latin word 'fossilis' which means 'dug up'. A fossil is the remains or impression of any plant or animal which has been buried in sediment and preserved in a sedimentary rock. Less commonly, fossils can also be preserved in ice, e. There are two main kinds of fossil: a body fossil which is the actual remains of a plant or animal and a trace fossil, which records the activities of the animal, like footprints, burrows and bit marks.

How do fossils form? In principal forming a fossil is quite easy. A plant or animal just has to get buried in sediment. Sadly the process is not that simple.

They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. Temperature, pressure and chemically active fluids can alter existing rocks while still in the solid state to produce new rocks and sometimes minerals that are stable under the new conditions. These are the metamorphic rocks. There are two types of metamorphic rocks. Those that show the effects of pressure by some parallel structure within the rock like layering or parallel alignment of mineral grains or banding.

These are the Foliated metamorphic rocks. All of the other metamorphic rocks those without parallel structures are call Non Foliated. The two basic types of metamorphic rocks are: foliated and non foliated. Foliation can be observed in the field by parallel bands within the rocks or it can often be observed on a smaller scale in the hand specimen.

This foliation can also be seen microscopically by the alignment of platy minerals. Non foliated as the name implies, does not have any parallel orientation of the grains within the metamorphic rock. Non foliated rocks have recrystallized without producing parallel structures. This can be done in the absence of pressure but more commonly by the lack of elongate or tabular grains.

For example sandstone is metamorphosed into quartzite by the normal agents of metamorphism heat and pressure , but because of the equidimensional nature of the quartz grains, no alignment or parallel structure can take place. Low grade — Rocks that are metamorphosed under temperature and pressure conditions up to o C and Mpa. High grade — Rocks that are metamorphosed under temperature and pressure conditions higher than about o C and Mpa.

Migmatite — The result of a composite rock, part igneous and part metamorphic. Types of metamorphism. Contact metamorphism — Metamorphism that occurs when rocks are heated and chemically changed adjacent to an intruded body of hot magma.

Burial metamorphism — Meta morphism that occurs after diagenesis, as a result of the burial of sediments in deep sedimentary basins. Regional metamorphism — Metamorphism of an extensive area of the crust , associated with plate convergence, collision, and subduction. Sedimentary Rocks. Sedimentary rock is one of the three main rock groups the others being igneous and metamorphic rock.

The sediments are then compacted and converted to rock by the process of lithification. Sedimentary rocks form in two basic ways. One type of sedimentary rock forms at the expense of existing rocks. Existing rocks are broken down by the processes of weathering and erosion. They are then deposited and lithified to form sedimentary rocks. These sedimentary rocks are called Detrital. The other method of sedimentary rock formation is by chemical precipitation. These are call the Chemical sedimentary rocks.

For example the evaporation of sea water can produce a sedimentary deposit of salt, gypsum and even limestone. Sedimentary rocks are derived from pre-existing rocks. The processes of weathering and erosion weathering occurs in situ, or "with no movement", and thus should not to be confused with erosion, which involves the movement and disintegration of rocks and minerals by agents such as water, ice, wind, and gravity , break rocks down through a variety of mechanical and chemical means.

Titanium can take single hits from high-caliber bullets, but it shatters and becomes penetrable with multiple hits from military-grade, armor piercing bullets.

Most guns legally bought and owned by individuals will likely not penetrate titanium. Rings made from titanium do not tarnish, therefore they will not give you a green ring around your finger. Titanium is significantly stronger than both aluminium and magnesium, although its higher density means that strength-to-weight ratios for the three metals tend to be similar. Titanium is not stronger than a diamond.

In terms of hardness, Titanium is not harder than a diamond either. Diamond strength is around 60 GPa.

As for the hardness scale, titanium is 36 Rockwell C, while diamond is Extra-hard alloys Its tensile strength to density ratio is the highest among all metals, beating tungsten, which, however, scores higher than titanium on the Mohs scale. As a natural metal with the highest tensile strength, tungsten is often combined with steel and other metals to achieve even stronger alloys.

Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Social studies What type of metamorphic rock has mineral grains that are arranged randomly?

Social studies. Ben Davis February 22, What type of metamorphic rock has mineral grains that are arranged randomly? What are the characteristics of a foliated metamorphic rock? How are the grains arranged in a non foliated metamorphic rock?

Which type of metamorphic rock has its grains arranged in bands? What are 5 examples of metamorphic rocks?

Why are metamorphic rocks the hardest? What is the weakest rock?