Scolecite

Key takeaways

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

Reference excerpt

Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, CaAl2Si3O10·3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium. There is an absence of barium, strontium, iron and magnesium. Scolecite is isostructural (having the same structure) with the sodium-calcium zeolite mesolite and the sodium zeolite natrolite, but it does not form a continuous chemical series with either of them. It was described in 1813, and named from the Greek word, σκώληξ (sko-lecks) = "worm" because of its reaction to the blowpipe flame.

Crystal class It is monoclinic m with space group Cc, but crystals are pseudotetragonal. Scolecite, like natrolite and mesolite, usually occurs as acicular (needle-like) and fibrous aggregations. It has nearly the same angles between the crystal faces as does natrolite, but natrolite is orthorhombic and scolecite is monoclinic. The etched figures (figures that arise from the action of a solvent on a crystal face, and indicate its true symmetry) and the pyroelectric character of scolecite show that it crystallizes with a plane of symmetry, but no axis of symmetry, that is to say it belongs to the hemihedral class of the monoclinic system. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicol prisms. Twinning on the ortho-pinacoid is usually evident.

Structure The structure of the aluminosilicate framework is the same for scolecite, natrolite and mesolite. Scolecite has long ordered chains, rotated 24° round the axis of the chain. One Ca cation and three H2O molecules are in four ion sites in the channels parallel to the c crystal axis. There is no sign of aluminium ions occupying silicon ion sites.

Unit cell Scolecite is a monoclinic mineral, with the angle β equal to about 109° and four formula units per unit cell (Z = 4). Described in this way, various sources give the following values for the parameters of the unit cell, which has one long side and two short ones:

a = 6.516 to 6.517 Å, b = 18.948 to 18.956 Å, c = 9.761 to 9.765 Å, β = 108.86 to 108.98° a = 6.52 to 6.53 Å, b = 18.96 to 18.97 Å, c = 9.76 to 9.78 Å, β = 108.9° a = 6.516 Å, b = 18.948 Å, c = 9.761 Å, β = 108.98° Crystals, however, are pseudotetragonal, and this can be represented by taking a different unit cell, with twice as many formula units (Z = 8) and two long sides and one short one. The axes are redefined, a and b are very nearly equal and the angle β between the new a and c axes is very nearly equal to 90° (a truly tetragonal crystal would have a = b and β = 90° exactly). The sources give the following values:

a=18.488 to 18.508 Å, b=18.891 to 18.96 Å, c=6.527 to 6.548 Å, β = 90.64 to 90.75° a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å β = 90.64° a = 18.508(5) Å, b = 18.981(5) Å, c = 6.527(2) Å, β = 90:64(1)° a = 18.51 Å, b = 18.97 Å, c = 6.53 Å, β = 90.6°

Crystal habit

Scolecite commonly occurs as sprays of thin, prismatic needles, frequently flattened on one side, with slanted terminations and striated parallel to the length of the needles. The crystals appear to be pseudo-orthorhombic or pseudo-tetragonal, and may be square in cross section. It also occurs as radiating groups and fibrous masses. Epitaxial intergrowths (intergrowths of two different crystalline substances in a non-random way) with mesolite, Na2Ca2Al6Si9O30·8H2O, are common. (Natrolite, Na2Al2Si3O10·2H2O, does not directly form epitaxial overgrowths on scolecite). All three minerals may be developed in the same crystal. Scolecite crystals appear to be monoclinic by X-ray analysis. Common forms include {111}, {111}, {101}, {110} and {010}.

Physical properties Scolecite is usually colorless or white, but can also be pink, salmon, red or green. It is transparent to translucent, with a white streak and a luster which is vitreous, or silky for fibrous specimens. It has a Mohs hardness of 5 to 5+1⁄2 and a specific gravity in the range 2.16 to 2.40. (2.24 to 2.31 2.25 to 2.29 2.16 to 2.4 2.25 to 2.31). Cleavage is perfect in two directions parallel to the length of the crystals; the mineral is brittle with an irregular fracture. Twinning is common on {100}, twin axis [001], as penetration or contact twins producing V-shaped or fishtail terminations. Scolecite is pyroelectric and piezoelectric, sometimes fluorescent yellow to brown in longwave and shortwave ultraviolet light. It is soluble in common acids. Not radioactive.

Optical properties Biaxial (-) with refractive indices: Nx = 1.507 to 1.513, Ny = 1.516 to 1.520, Nz = 1.517 to 1.521. Pleochroism has been reported, X: colorless Y: colorless Z: colorless.

Environment Scolecite is a common zeolite. It is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities (cavities filled with secondary minerals) of weathered basalts, also in gneisses and amphibolites, and in laccoliths and dikes derived from syenitic and gabbroic magmas, and in contact metamorphic zones. It is a hydrothermal mineral derived from low temperature alteration of basalts and related rocks, associated with other zeolites, calcite, quartz and prehnite. It can be found on top of the calcium zeolites heulandite, stilbite and epistilbite. Associated minerals include quartz, apophyllite, babingtonite, heulandite, stilbite and other zeolites.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Scolecite

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

In research: Scolecite 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 Scolecite 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: Scolecite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Calcium minerals, Minerals in space group 9, so understanding it makes those chapters shorter.
In everyday life: Look for Scolecite 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.

How to study Scolecite in 20 minutes

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

Frequently asked questions

What is Scolecite in simple terms?

Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, CaAl2Si3O10·3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium.

Why does Scolecite 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 Scolecite?

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 Scolecite.