Question

Which of the following minerals is found in its single-element form in the Earth's crust?

• A. Feldspar
• B. Quartz
• C. Graphite
• D. Pyroxene

Answer 1

Answer:

C. Graphite

Minerals in Elemental Form

Graphite

• Graphite is a naturally occurring form of the element carbon.
• It is one of the most common allotropes of carbon, the other being diamond.
• Unlike many other minerals which are compounds of various elements, graphite is found in its native state, meaning it exists as a pure element (carbon) in the Earth's crust.
• This elemental form is a key characteristic differentiating it from minerals like iron ore (hematite, Fe2O3), copper (often found as sulfides or oxides), or gold (though gold is also found natively, graphite is a more common example discussed in this context for its elemental nature).

Occurrence and Formation

• Graphite is formed through the metamorphism of organic matter under high pressure and temperature deep within the Earth.
• It can also be found in igneous and metamorphic rocks.
• Major graphite deposits are found in countries like China, India, Brazil, and North Korea.

Industrial Significance

• Lubricant: Its layered structure allows the layers to slide easily over each other, making it an excellent dry lubricant.
• Refractory Material: Graphite has a high melting point (sublimes at around 3652 °C) and is resistant to thermal shock, making it useful in crucibles and furnace linings.
• Electrodes: It is a good conductor of electricity and is used in batteries and electroplating.
• Pencils: The 'lead' in pencils is actually a mixture of graphite and clay.

Distinction from Other Minerals

• Many economically important minerals are compounds, such as oxides (e.g., Hematite - iron oxide), sulfides (e.g., Pyrite - iron sulfide), or silicates (e.g., Quartz - silicon dioxide).
• Graphite's occurrence as a native element distinguishes it in mineralogy and geology. While native gold and copper also exist, graphite is a prime example when discussing common minerals found in their elemental form in the crust.