Lindley Hanson's List: Rocks and Minerals

The Mineralogy Database was last updated on 3/8/09 and it contains 4,442 individual mineral species descriptions with links and a comprehensive image library. Visit the "What's New" section for details.

Each mineral has a page linked to tables devoted to crystallography, crystal structures, X-Ray powder diffraction, chemical composition, physical and optical properties, Dana's New classification, Strunz classification, mineral specimen images, and alphabetical listings of mineral species. There also are extensive links to other external sources of mineral data and information.

Objective

In this science fair project you will investigate how the presence of seed crystals changes the growth rate of rock candy.

Introduction

Have you ever looked at rock candy and wondered how it's made? Rock candy is actually a collection of large sugar crystals that are "grown" from a sugar-water solution. Sugar, like many other materials, can come in many different physical states. As a solid it can either be amorphous, without shape, like when it forms cotton candy, or crystalline, with a highly ordered structure and shape, like when it forms rock candy crystals.

Crystals form when the smallest particles of a substance, the molecules, arrange themselves in an orderly and repetitive pattern. Molecules are too small for us to see moving around and arranging themselves, but you can get a rough idea of what this would look like by taking a small shallow tray and filling it with marbles, ball bearings, or other spheres. As you add more spheres, the bottom of the tray becomes covered, then the spheres must form layers on top of one another, and a structure or pattern emerges.

So how do the molecules of a substance get together to form a crystal? First there have to be enough molecules in one area that they have a high chance of bumping into one another. This happens when a solution, which is made up of a liquid and the compound that will be crystallized, is saturated. In the rock candy, the liquid is water and the compound is sugar. A solution is saturated when the liquid holds as much of the compound dissolved in it as possible. For example, when making rock candy, you dissolve as much sugar as possible in water to make a saturated solution. If you add more compound than can dissolve in the liquid, the undissolved bits remain as solids in the liquid. In a saturated solution, the molecules bump into one another frequently because there are so many of them. Occasionally when they bump into each other, the molecules end up sticking together; this is the beginning of the crystallization process and is called

Mineral mix and match

Minerals are everywhere. Different properties of minerals make them useful for different reasons. Have a go matching properties to minerals and objects, match minerals to objects, or just take it easy and refresh your memory of the minerals around you.

Explanation of what causes color in minerals

Everything you'd want to know about quartz and its geologic environment.

So, what exactly are alkaline rocks? In a broad sense, these are the rocks that form from magmas and fluids so enriched in alkalis that they precipitate sodium- and potassium-bearing minerals not usually found in "normal" rocks (like feldspathoids, aegirine and sodic amphiboles). Magmas rapidly chilled to glassy rocks during volcanic eruptions may not actually contain any of these minerals, but will certainly turn up alkali-rich components in their normative composition, i.e. chemical analysis recalculated to a standard set of components which approximate real minerals: normative nepheline = NaAlSiO4, normative aegirine (a.k.a. acmite) = NaFeSi2O6, etc. In addition to alkalis, these rocks contain elevated levels of those trace elements whose ionic radius is either too large or too small in comparison with more common elements in the same oxidation state. This difference in radius precludes extensive substitution of over- and undersized trace elements in the structure of common rock-forming minerals (olivine, plagioclase, pyroxenes, micas, etc.), making them incompatible with respect to these minerals. Actually, the term "incompatible" is somewhat misleading here because some alkaline magmas and fluids contain such high levels of these elements that they form their own mineral phases and, thus, become perfectly compatible in these specific magma compositions. Alkaline rocks may comprise several volumetric per cent or more of minerals containing essential Zr, rare-earth elements (REE), Nb, Sr, Ba, or Li: eudialyte, loparite, lamprophyllite, noonkanbahite, baratovite, etc. These minerals are either exceedingly rare or not present at all in other rock types. Different groups of alkaline rocks are enriched in specific incompatible trace elements and may also show either prevalence of Na over K or vice versa. For example, lamproites are rich in K, Sr and Ba, but generally poor in Nb. Needless to say, these chemical differences are reflected in the mineralogical makeup of alkaline rocks.

Mindat.org is the largest mineral database and mineralogical reference website on the internet. This site contains worldwide data on minerals, mineral collecting, mineral localities and other mineralogical information.

Giant dikes typically exceed 30 m in width and 100 km in length, with some examples over 100 m wide and 1,000 km long. Dikes are self-induced magma-filled fractures, and they are the dominant mechanism by which basaltic melts are transported through the lithosphere and the crust. These spectacular intrusions are likely to have fed flood basalts in large igneous provinces (LIPs), including provinces where the surface basalts have been diminished or removed by erosion.

Although giant dikes can intermingle with denser swarms of smaller dikes of similar composition (and probably similar origin), others occur in sets of several to a few dozen extremely large quasi-linear or co-linear intrusions, which may gently bend and converge/diverge at low angles across many degrees of latitude. Tectonic controls on the formation of giant dikes appear to be independent and different from structures related to smaller dike swarms. Theoretical modeling and field observations help us to understand the essential physics of magma migration from its source to its final destination in the upper lithosphere.

This discussion focuses on geographic patterns, magma parameters, and associated physical features that provide evidence and arguments about the origins of giant dikes. In particular, we describe how giant dikes may be tectono-magmatic features of lithospheric plates, not necessarily resulting from deep-mantle plumes.