science

Theralite

Theralite is a 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 Theralite rather than just read about it. In short: Theralite (from Greek "to pursue") is, in petrology, the name given to calcic foidal gabbro, a holocrystalline plutonic rock consisting of augite, olivine, calcic plagioclase (labradorite), and nepheline, along with accessories including biotite, magnetite, ilmenite and analcime. Theralite is the intrusive equivalent of nepheline basanite (a foidal basaltic rock with essential calcic plagioclase and essential olivin…

Key takeaways

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

Reference excerpt

Theralite (from Greek "to pursue") is, in petrology, the name given to calcic foidal gabbro, a holocrystalline plutonic rock consisting of augite, olivine, calcic plagioclase (labradorite), and nepheline, along with accessories including biotite, magnetite, ilmenite and analcime. Theralite is the intrusive equivalent of nepheline basanite (a foidal basaltic rock with essential calcic plagioclase and essential olivine). With the increase in silica (SiO2) and the concomitant reduction in nepheline, theralite becomes gabbro. With a decrease in silica and reduction in olivine theralite grades into teschenite and with the addition of sodic feldspar, grades into essexite. With a further reduction in silica such that there is no feldspar these rocks become melteigites. With the addition of alkali feldspar replacing or becoming more dominant than calcic plagioclase theralites grade into foidal syenite, including shonkinite. Pyroxene in these rocks may be of green colour or purplish-brown and rich in titanium. Properly theralite is only for a specific type of calcic foidal gabbro, those with essential nepheline and without essential analcime or sodic feldspar.

Occurrence Theralite occurs, for example, at Lugar Sill, Scotland,, in the Kamarbon alkaline gabbroic intrusion in Iran, and at the Crazy Mountains, Montana.

Teschenites Teschenites were once considered part of the theralite group. They contain essential pyroxene, olivine and analcime rather than nepheline. Modern petrology would classify the teschenites as an analcime-bearing gabbro. They are petrogenetically unrelated to nepheline gabbros as analcime is not produced by the same genetic processes.

Essexites Essexite is a form of silica-undersaturated pyroxene gabbro, containing nepheline and orthoclase as essential constituents, though often in small proportions. Essexites can be considered to represent the intrusive equivalent of an alkaline basalt. Essexites are usually associated with other alkaline, silica undersaturated to monzonitic intrusive rocks and coeval high-alumina basalts. Essexites are no longer considered part of the theralite group and are more properly known as nepheline monzogabbro or nepheline monzodiorite. The presence of orthoclase indicates a petrogenetic difference with nepheline gabbros.

References

Bibliography This article incorporates text from a publication now in the public domain: Flett, John Smith (1911). "Theralite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 26 (11th ed.). Cambridge University Press. pp. 791–792. This contains more detailed analytic and location data. theralite (mineral)- Britannica Online Encyclopedia| [1] Heinrich, Microscopic Petrography, McGraw-Hill, 1956

Illustrations

Worked examples

Example 1 — a first encounter with Theralite

Start with the simplest possible case. Write down what Theralite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Theralite 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 Theralite 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 Theralite

In research: Theralite appears in 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 Theralite 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: Theralite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Igneous petrology, Igneous petrology stubs, Plutonic rocks, so understanding it makes those chapters shorter.
In everyday life: Look for Theralite 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 Theralite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Theralite 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 Theralite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Theralite in simple terms?

Why does Theralite matter?

Because it connects several 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 Theralite?

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 Theralite.