Please Be Gneiss Trivia Quiz

Answer: metamorphic

Unlike other varieties of coal, anthracite is classified as a metamorphic rather than a sedimentary rock. It is, indeed, the hardest variety of coal, with the highest carbon content and highest energy density. Also known as "black coal", it is also a rare commodity, accounting for about 1% of the world's total coal production. Some of the largest anthracite deposits are found in the Coal Region of northern Pennsylvania in the US.

Though slower to ignite than bituminous coal, anthracite burns cleanly with a blue flame, without producing soot or toxic fumes, while releasing a high amount of energy - which makes it prized as fuel for the heating of residential and office buildings. However, due to its rarity, it is also considerably more expensive than ordinary coal. Besides its uses in steel-making and other industries, these days anthracite is widely employed in large-scale water filtration systems.

The name "anthracite" means "coal-like" in Greek. With its dark, glossy appearance, it is quite similar to jet - which is a type of lignite, a sedimentary rock, and the lowest grade of coal.

Answer: igneous

Basalt is an extrusive igneous rock, formed from the rapid cooling of low-viscosity, mafic lava (i.e. lava rich in iron and magnesium, but with relatively low silica content). In terms of appearance, it is fine-grained (aphanitic), hard, and usually very dark in colour. It is estimated that about 90% of the volcanic rock present on Earth's surface is basalt; this rock is also widespread on other planets in the solar system, such as Venus and Mars.

Most of the basalt on Earth is formed by decompression melting of the mantle (the layer between the crust and the outer core). When cooling, flows of basaltic lava often fracture, creating distinctive structures called columns, with polygonal cross-sections: the slower the cooling, the larger the columns. The world's most famous columnar basalt flow is the UNESCO World Heritage Site of Giant's Causeway in Northern Ireland. When basaltic lava erupts underwater, it forms rounded shapes known as "pillow basalt".

The name "basalt" comes from the misspelling of "basanites", a Latin word of Greek origin meaning "very hard stone" - which is an apt description of this rock. Basalt is used as construction material, and also in sculpture: the famous Code of Hammurabi was engraved on a basalt stele.

Answer: metamorphic

Probably the best-known of all metamorphic rocks, marble is the result of the metamorphism of sedimentary carbonate rocks such as limestone or dolomite. This process modifies the original structure of the sedimentary rock, creating a distinctive pattern of interlocking carbonate crystals. The veins found in many marble varieties (from which the word "marbling" comes) are due to the presence of impurities in the protolith (the original sedimentary rock), which have been transformed by intense heat and pressure. On the other hand, the pure white marble (such as the famed Carrara marble) so highly prized in sculpture and architecture is the result of the metamorphism of limestone with a very low silicate content. Because of its origins as a carbonate rock, marble is vulnerable to acids - including acid rain, which is particularly damaging to outdoor marble structures.

The word "marble" comes from the Ancient Greek "mármaros", meaning "rock that sparkles"; the name of the Sea of Marmara is related to this Greek word. Marble has been a favourite stone for carving and sculpting since antiquity because of its relative softness and characteristic luster. Turkey is presently the world's largest exporter of marble, followed by Italy and Greece.

Answer: sedimentary

Chalk is a sedimentary rock that consists of almost pure calcite, a calcium carbonate mineral. Soft, pale-coloured, and porous, it was formed in the Cretaceous period (145-66 million years ago) by the compression of plankton that had settled on the sea floor. Though similar in appearance to minerals such as gypsum and diatomite, chalk is considerably harder, and reacts to acid by producing effervescence. Another distinctive feature of chalk is its fossil content, due to its organic origin.

Chalk deposits and cliffs are common in parts of Western Europe, especially in southern England (the famed White Cliffs of Dover) and in France, on the other side of the English Channel; in the Champagne region, the caves where the prized sparkling wine is stored are built in the underlying chalk soil.

Besides the white or coloured sticks used for writing or artistic pursuits, chalk is one of the main ingredients of putty, as well as a source of quicklime. The Cretaceous period, in which most chalk deposits were formed, was named after "creta", the Latin word for chalk. The English name comes from the Latin "calx", meaning "limestone".

Answer: sedimentary

The name dolomite denotes both a mineral composed of calcium magnesium carbonate, and a sedimentary rock (sometimes referred to as "dolostone") that contains at least 50% of this mineral. Dolomite forms from calcite (one of the main components of limestone) by a process known as "dolomitization", in which magnesium ions replace calcium ions. As a rock, it is relatively soft, with a finely granular texture; it is also pale-coloured, though it weathers to a darker colour due to the presence of iron. Dolomite does not react as readily as limestone to dilute hydrochloric acid, and cannot be substituted for limestone in chemical processes that require a high calcium content. On the other hand, it can be employed in producing magnesium chemicals, such as Epsom salt. Dolomite is also used as a building and ornamental stone.

Dolomite owes its name to 18th-century French geologist Déodat Gratet de Dolomieu, who first described the rock in 1791 after he discovered it during a visit to the Alpine mountain range that now separates Italy from Austria. A few decades later, those beautiful mountains - also known as "Pale Mountains" - were named Dolomites.

Answer: metamorphic

Formed by high-temperature and high-pressure processes from igneous or sedimentary rocks, gneiss is one of the most common types of metamorphic rock. It is characterized by alternating lighter- and darker-coloured bands, referred to as gneissic banding. However, unlike other metamorphic rocks, it does not readily fracture along those layers. Darker bands contain minerals with a higher content of magnesium and iron (mafic), while the lighter ones contain felsic minerals such as feldspar and quartz. Some gneiss formations are among the oldest rocks on Earth: one of them is the Acasta Gneiss, an outcrop in Canada's Northwest Territories that metamorphosed 3.58 to 4.031 billion years ago.

The name "gneiss" comes from the Middle High German "gneist", meaning "spark" - a reference to the rock's glittering appearance; it is pronounced "nice" - hence this quiz's punny title. A particular variety of gneiss, called Facoidal gneiss, is found around Rio de Janeiro, where it has been extensively used as construction material for many of the city's historic buildings.

Answer: igneous

Granite is an intrusive (or plutonic) igneous rock - meaning that, unlike basalt or pumice, it is not the product of a volcanic eruption, but is formed when magma penetrates existing rock and solidifies underground. A coarse-grained (phaneritic) rock, composed mostly of quartz and feldspar, granite is the most abundant basement rock on Earth. Granite's granular texture is uniformly coarse; the matrix (groundmass) tends to be lighter in colour, peppered with spots of darker minerals such as mica. The family known as granitoids, or granitic rocks, comprises a large number of igneous rocks that contain quartz, plagioclase feldspar and alkali feldspar in varying proportions.

The name "granite" comes from the Latin "granum", meaning "grain" - a reference to the rock's characteristic structure. Widely used since Ancient Egyptian times, granite is highly prized as a construction material because of its hardness and toughness; it is now much easier to work than in the past thanks to the availability of modern tools. Due to its particular features, granite is also a favourite surface for rock climbing.

Answer: sedimentary

Limestone is a sedimentary rock consisting mainly of calcite and aragonite, two of the most common mineral forms of calcium carbonate. It forms when these minerals precipitate out of water that contains dissolved calcium. Many limestone deposits are extremely ancient, some dating back to almost 3 billion years ago; most of them were formed in shallow marine environments, especially those with warm waters, where living organisms are most active. Being partially soluble, especially in acidic substances, limestone is prone to erosion, forming distinctive landforms known as karsts.

With its worldwide distribution, limestone is one of the oldest construction materials employed by humankind (the Great Pyramid of Giza is entirely covered in limestone blocks), and is still frequently used, especially in regions where it abounds. Another of the stone's major uses is as a source of lime (calcium oxide), a chemical compound essential in the manufacturing of cement and mortar.

Answer: igneous

The term "porphyry" refers to a particular texture of some igneous rocks (such as andesite), characterized by large, coarse crystals (phenocrysts) embedded in a fine-grained, silicate-rich matrix (groundmass). This is due to the process of fractional crystallization occurring in magma before it is erupted to the surface as lava. The larger crystals typical of the porphyritic texture are generally feldspar (an aluminum tectosilicate mineral) or quartz (a silicate mineral).

Though it can come in a variety of colours, as its name suggests (from the Greek "porphyra", meaning "purple"), porphyry is often identified with the purplish-red stone that was highly sought after in antiquity, both for architectural and decorative purposes. Because of its colour, the Romans called the stone "imperial porphyry": it was mined from a quarry located in the Eastern Desert of Egypt. Porphyry was used for imperial sarcophagi both in Rome and Byzantium; this use continued in the Middle Ages and also in more recent times. The sarcophagus of Arthur Wellesley, Duke of Wellington, was carved from a single piece of Cornish porphyry.

An impressive natural monument made primarily of porphyry (though not the imperial variety) is the butte known as Devil's Tower in the US state of Wyoming.

Answer: igneous

Like obsidian, another well-known product of volcanic activity, pumice is a kind of volcanic glass, lacking crystalline structure. However, both of them are generally classified as igneous rocks. Pumice is produced during explosive eruptions, when the bubbles formed by volcanic gases within viscous magma remain during the cooling process. The tiny cavities in the stone are known as vesicles. Lightweight and generally light-coloured, with very low density, pumice is the only stone that will float on water. Underwater eruptions can create very large pumice rafts, which are a hazard for ships.

The name "pumice" comes from Latin "pumex", which is related to "spuma", meaning "foam" - a reference to the stone's distinctive appearance and texture. Found all over the world, pumice is particularly abundant in places with high volcanic activity - such as the countries around the Pacific Ring of Fire, the Caribbean, and parts of the Mediterranean region. Pumice finds many uses in cleaning, personal care, and construction - especially as a key component of lightweight concrete, such as the one used to build the famed dome of the Pantheon,

Answer: metamorphic

Quartzite (from the German "Quarzit") is pure quartz sandstone metamorphosed through tectonic compression. Unlike other metamorphic rocks, it shows no foliation (layering). In its pure form it is white to grey, while different colours are due to the presence of minerals such as haematite. Quartzite is a very hard rock, composed of tightly interlocked quartz crystals, with a grainy surface and glassy appearance. As a product of orogeny, it is often found in mountain areas such as the Scottish Highlands; Mozambique's highest mountain, Monte Binga, is composed of hard, grey Precambrian quartzite.

In prehistoric times, quartzite was one of the rocks used to make stone tools and weapons. Now its most common practical use is as a decorative stone, particularly for roof tiles and kitchen countertops - in the latter case, as a durable and stain-resistant (though more expensive) alternative to granite.

Answer: sedimentary

As its name implies, sandstone is a clastic sedimentary rock - composed of fragments (in this case, having the size of very fine grains of sand) of older, weathered or eroded rocks. This material, transported by wind or water, form deposits that gradually accumulate, undergoing physical and chemical changes that turn them into rock (lithification). Amounting to about one-fifth of all sedimentary rocks, sandstone is composed of silicate minerals - mostly quartz and feldspar. Like sand, it comes in a wide range of colours, depending on the impurities contained in the minerals.

Some well-known sandstone formations owe their red colour to the presence of haematite (ferric oxide): many of these are located in the southwestern US, but Uluru, in Australia's Northern Territory, is one of the largest in the world.

Sandstone has been employed as a construction material since prehistory. Most of the buildings of the ancient city of Petra in Jordan - nicknamed the "Rose City" - were carved into the reddish sandstone of the surrounding cliffs. Some of Australia's oldest higher education institutions are called "sandstone universities", as most of their buildings are made of sandstone. Though easy to work, sandstone is not always resistant to weathering, and may require frequent repairs.

Answer: sedimentary

A member of the large class of clastic sedimentary rocks known as mudrocks, shale is formed from mud composed of a mix of clay minerals (such as kaolin) and tiny fragments of other minerals. Shale's distinctive feature is its fissility - that is, the tendency to split into very thin layers known by the Latin term "laminae". It is the most common of sedimentary rocks, and a common source of petroleum and natural gas - particularly abundant in shale beds that contain high proportions of organic matter. Shale is usually grey, though the colour may be altered by the presence of small amounts of other minerals. Black shale is rich in unoxidized carbon, and can contain heavy metals such as uranium and zinc.

The name "shale" is of Germanic origin, and is related to both "scale" and "shell". Shale is the parent rock of a number of metamorphic rocks, such as schist, which is also characterized by foliation - the quality of easily splitting into thin flakes or plates.

Answer: metamorphic

Slate originates from the metamorphism of shale and other mudrocks. Very fine-grained and often dark grey (though not exclusively so) in colour, slate is characterized by foliation known as "slaty cleavage", which enables the rock to split into smooth, flat sheets when struck with specialized tools. Chemically, slate is mainly composed of quartz and the clay minerals chlorite and illite, with traces of other minerals that may affect the rock's colour. Slate is mined in many parts of the world; slate extraction is a particularly important industry in Spain, UK, US, and Brazil.

The name "slate" comes from Old French "esclate", meaning "splinter" - an apt description of a rock that can be easily split into thin layers. Though now primarily used as roofing material, in the past it was widely used as a writing surface - hence phrases such as "clean slate" or "blank slate".

Answer: igneous

Tuff consists of volcanic ash ejected during an eruption that has undergone lithification - that is, it has become solid rock. Though the process by which tuff is formed is similar to that of sedimentary rocks, it is generally classified as an igneous rock because of its pyroclastic (volcanic) origin: true tuff contains at least 75% ash. Tuff can have different chemical compositions, according to the type of magma from which it derives. This also influences its colour, as tuff from mafic magma (basaltic tuff) is darker than that from felsic magma (rhyolitic tuff), which is usually brownish-yellow or greyish-brown.

The name "tuff" comes from the Latin "tophus" via the Italian "tufo". Being soft and relatively lightweight, it has been used as a construction material for thousands of years. The famous "moais" of Easter Island are carved out of basaltic tuff. As tuff is quite common in Italy, the Romans used the stone extensively in many kinds of buildings, especially the brown or grey variety known as "peperino". Tuff should not be confused with the similarly-named tufa, which is a sedimentary rock, a variety of limestone.