earth science

Zigrasite

Zigrasite 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 Zigrasite rather than just read about it. In short: Zigrasite is a phosphate mineral with the chemical formula of MgZr(PO4)2(H2O)4. Zigrasite was discovered and is only known to occur in the Dunton Quarry at Oxford County, Maine.

Key takeaways

Zigrasite 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 Zigrasite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Zigrasite from memory before moving on to harder problems.

Reference excerpt

Zigrasite is a phosphate mineral with the chemical formula of MgZr(PO4)2(H2O)4. Zigrasite was discovered and is only known to occur in the Dunton Quarry at Oxford County, Maine. Zigrasite was specifically found in the giant 1972 gem tourmaline-bearing pocket at the Dunton Quarry. Zigrasite is named after James Zigras who originally discovered and brought the mineral to attention.

Occurrence Zigrasite is found in association with tourmaline, microcline, quartz, albite, beryl, amblygonite-montebrasite, childrenite-eosphorite, and apatite. It is crystallized as one of the last minerals during pocket formation. The crystals themselves were found perched on a crystal of tourmaline from the giant 1972 pocket at the Dunton Quarry. The quarry itself is located in a complex rare-element granitic pegmatite that has produced large quantities of gem tourmaline as well as many other rare phosphate species.

Physical properties Zigrasite is an offwhite to pale yellow or light tan in color. Zigrasite exhibits a vitreous luster, and a white streak. The Mohs hardness is 3. The measured (Berman Balance) and calculated densities are 2.76(4) and 2.66 g/cm3 respectively. Zigrasite exhibits imperfect cleavage in two directions, parallel to (010) and (001), it shows no parting, is brittle and has hackly fracture. In transmitted light zigrasite is colorless and non-pleochroic, biaxial negative with indices of refraction α 1.597(1) β 1.622 (1), γ 1.635 (1). Zigrasite is translucent and shows a light blue to pale yellow cathodoluminescence.

Crystal structure Zigrasite's atomic coordination consists of two phosphorus sites which are solely occupied by phosphorus and tetrahedrally coordinated by four oxygen anions with <P-O> distances of 1.532 and 1.533 Å. There are also two magnesium, both of which are occupied solely by Mg and are octahedrally coordinated by two oxygen anions and four (H2O) groups with <Mg-O> distances of 2.064 and 2.075 Å. There is a single zircon site solely occupied by zircon and octahedrally coordinated by six oxygen anions with a <Zr-O> distance of 2.065 Å. The zircon octahedron shares corners with six (PO4) tetrahedra to form a pinwheel cluster. This cluster forms a fragment of a Zr(PO4)2 sheet which is parallel to the (001) direction. Alternating tetrahedra point up and down relative to the plane of the sheet. Isolated Mg(H2O)6) octahedra are arranged in layers parallel to (001). These layers are intercalated between the [Zr(PO4)2] sheets linking through the apical vertices of the (PO4) tetrahedra. This structure is formally a heteropolyhedral framework with linkage weaker in the c direction accounting for cleavage.

Chemical properties Zigrasite is one of three compositional variations in zircon phosphate grains from the giant 1972 tourmaline pocket, representing the magnesium phase with malhmoodite representing the iron phase and an as of yet unnamed calcium-analogue. Zigrasite can be considered to be the magnesium end member for the zircon phosphate grains found in the giant 1972 pocket. Zigrasite exhibits hydrogen bonding which increases linkage within the layer of magnesium octahedra.

Chemical composition

X-ray crystallography The powder-diffraction pattern was recorded with Cu-Ka X-radiation on a DebyeScherrer camera with a diameter of114.6 mm and a Gandolfi attachment. Refinement of the unit-cell parameters gave the following values: a = 5.321(7) Å , b = 9.360(10) Å , c = 9.660(8)Å , a = 97.38(10)º, b = 91.29(9)º, g = 90.58(9)º, V = 477.0(5) Å 3 . Unit-cell dimensions were also determined on a Bruker single-crystal diffractometer using graphite-monochromated Mo-Ka Xradiation and the resulting values (a = 5.3049(2) Å , b = 9.3372(4) Å, c = 9.6282(5) Å, a = 97.348(1)º, b = 91.534(1)º, g = 90.512(4)º) are in close agreement with those determined by powder diffraction.

See also List of MineralsList of minerals named after people

References

External links Dunton Quarry James Zigras Archived 2019-12-03 at the Wayback Machine

Illustrations

Worked examples

Example 1 — a first encounter with Zigrasite

Start with the simplest possible case. Write down what Zigrasite 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 Zigrasite 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 Zigrasite 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 Zigrasite

In research: Zigrasite 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 Zigrasite 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: Zigrasite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Minerals in space group 2, Phosphate minerals, Triclinic minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Zigrasite 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 Zigrasite in 20 minutes

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

Frequently asked questions

What is Zigrasite in simple terms?

Zigrasite is a phosphate mineral with the chemical formula of MgZr(PO4)2(H2O)4. Zigrasite was discovered and is only known to occur in the Dunton Quarry at Oxford County, Maine.

Why does Zigrasite 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 Zigrasite?

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 Zigrasite.