earth science

Picrite basalt

Picrite basalt is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Picrite basalt rather than just read about it. In short: Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite.

Key takeaways

Picrite basalt belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Picrite basalt to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Picrite basalt from memory before moving on to harder problems.

Reference excerpt

Picrite basalt or picrobasalt is a variety of high-magnesium olivine basalt that is very rich in the mineral olivine. It is dark with yellow-green olivine phenocrysts (20-50%) and black to dark brown pyroxene, mostly augite. The olivine-rich picrite basalts that occur with the more common tholeiitic basalts of Kīlauea and other volcanoes of the Hawaiian Islands are the result of accumulation of olivine crystals either in a portion of the magma chamber or in a caldera lava lake.[1] The compositions of these rocks are well represented by mixes of olivine and more typical tholeiitic basalt. The name "picrite" can also be applied to an olivine-rich alkali basalt: such picrite consists largely of phenocrysts of olivine and titanium-rich augite pyroxene with minor plagioclase set in a groundmass of augite and more sodic plagioclase and perhaps analcite and biotite. More generally the classification of fine grained rocks recognizes a group known as 'picritic rocks' that are characterised by high magnesium content and low SiO2 content. They fit in the TAS classification system only at the lowest level of SiO2 (41 to 43% by weight) and Na2O + K2O (up to 3% by weight). They include picrite, komatiite and meimechite. Picrites and komatiites are somewhat similar chemically (defined as >18% MgO), but differ in having 1 to 3% total alkalis and less than 1% total alkalis respectively. Komatiite lavas are products of more magnesium-rich melts, and good examples exhibit the spinifex texture.[2] They are largely restricted to the Archean. In contrast, picrites are magnesium-rich because crystals of olivine have accumulated in more normal melts by magmatic processes. Picrite basalt is found in the lavas of Mauna Kea and Mauna Loa in Hawaiʻi[3], Curaçao, in the Piton de la Fournaise[4] volcano on Réunion Island and various other oceanic island volcanoes.

Picrite basalt has erupted in historical times from Mauna Loa during the eruptions of 1852 and 1868 (from different flanks of Mauna Loa).[5] Picrite basalt with 30% olivine commonly erupts from the Piton de la Fournaise.[6] In addition to extrusive occurrences, it also occurs in minor intrusions.

Oceanite Oceanite is a variety of picritic basalt characterized by its large amounts of olivine phenocrysts and lesser amounts of augite and by having a groundmass of olivine, plagioclase and augite. The term was coined by Antoine Lacroix in 1923 for rare basalts with more than 50% olivine.[7]

Common uses Olivine basalt is commonly used by foundries, boilermakers and boiler users to protect the area around a burner tip or to protect a floor from molten metal and other slag. Its use in this fashion is appropriate since olivine is a highly refractory, high-melting-temperature mineral.

References

^Carmichael, Ian S. E.; Turner, Francis J.; Verhoogen, John (1974). Igneous Petrology. McGraw-Hill. pp. 406–426. ^ Metrich, Nicole; Pineau, Françoise; Javoy, Marc (1988). "Volatiles: Mantle Source Characterization and Degassing Process for Hot Spot Volcanism - The Piton de la Fournaise (Reunion Island) Example". Archived from the original on 8 November 2005. {{cite journal}}: Cite journal requires |journal= (help) ^Kerr, A. C. (1997). "What is the difference between a komatiite and a picrite?". Archived from the original on 22 June 2004.. ^Le Maitre, L. E., ed. (2002). Igneous Rocks: A Classification and Glossary of Terms (2nd ed.). Cambridge. p. 118. ^Rhodes, J. M. (1995). "The 1852 and 1868 Mauna Loa Picrite Eruptions". Geophysical Monograph Series. 92. American Geophysical Union. Retrieved 18 February 2006. Wilkinson, J. F. G.; Hensel, H. D. (1988). "The petrology of some picrites from Mauna Loa and Kilauea volcanoes, Hawaii". Contributions to Mineralogy and Petrology. 98 (3): 326–345. Bibcode:1988CoMP...98..326W. doi:10.1007/bf00375183. S2CID 115132181. ^Williams, Howel; Turner, Francis J.; Gilbert, Charles M. (1954). Petrography. W. H. Freeman. pp. 40–41.

Illustrations

Worked examples

Example 1 — a first encounter with Picrite basalt

Start with the simplest possible case. Write down what Picrite basalt claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Picrite basalt before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Picrite basalt ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Picrite basalt

In research: Picrite basalt appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Picrite basalt in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Picrite basalt is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aphanitic rocks, Basalt, Mafic rocks, so understanding it makes those chapters shorter.
In everyday life: Look for Picrite basalt outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Picrite basalt in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Picrite basalt means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Picrite basalt out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Picrite basalt in simple terms?

Why does Picrite basalt matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Picrite basalt?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Picrite basalt.