FMF - Friends of Minerals Forum, discussion and message board

[Screenname]

When do they stop and growing and is it possible to own one that is still growing? There is a pic on here of an early stage crystal that is still young, I am sure you have all seen it by now. Would something like this continue to grow if in the right conditions? And what that cave in Mexico with quartz crystals the size of telephone poles, how long would it take one to get that big and when crystals are in a cave like that are they still growing?

[Jesse Fisher]

Crystals will stop growing when the conditions that feed their formation (proper temperature, pressure, and solution chemistry) change to the extent that they no longer have the ability to obtain the chemical nutrients necessary. For minerals such as quartz, which are made up of covalently bonded atoms, the conditions of formation are usually well beyond anything that can be replicated by the average individual. Salts (minerals made up of ionically bonded atoms from an aqueous solution) are more easily grown at temperatures and pressures found on the earth's surface. Crystal growing kits for things like alum and copper sulfate can be purchased for home use, and in this sense, you can "own" a growing crystal. Crystals can also be grown at home from concentrated solutions of table salt (sodium chloride) or sugar.

The large crystals in the Mexican caves (Naica Mine) are not quartz, but gypsum (hydrous calcium sulfate. I doubt that they are still growing, but Peter Megaw can likely tell you more about these.

[Screenname]

Thanks for the info. Now something on growing salt - can you grow an actual halite crystal from table salt, like the ones you find in nature, or can you only grow like the ones made from a concentration of salt water? I saw one recipe where you mix up some salt water and let the water evaporate and you end up with salt geodes but that's not like a natural salt crystal, Halite.

[Amir Akhavan]

The salt crystals you grow at home are not principally different from those in nature.
There are differences, but nothing fundamental, they are basically the same stuff.

If you call them "halite" is a different question. Some would (me), others wouldn't, because "man-made" does not fit the definition of a "mineral".

[kokoqn4o]

There aren't differences between halite and salt crystals in their chemical content (NaCl).
The difference is that the mineral halite is a creation of the nature and the salt crystal is human made.

[Carles Millan]

[marco campos-venuti]

Wow!!
The topic has veered in an interesting direction. The definition of "Mineral" is quite obsolete and strongly under revision.
Classic definition (from Wikipedia) is : "A mineral is a naturally occurring substance that is solid and inorganic representable by a chemical formula, usually abiogenic, and has an ordered atomic structure."
The 3 problems in this definition are:
1-natural (so manmade NaCl would not be a mineral, despite it is identical to nature-made)
2-inorganic (so biogenic aragonite of shells would not be a mineral until it would fossilize). But the fossilization process is arbitrarily defined as older than 1 million years.
3-Ordered structure (so opal, chalcedony and jasper that cover more than 50% of know varieties and fill more than 50% of all the mineral museum of the world, would not be minerals)
The problem is that if you accept all, mineralogists think that too many new minerals would born and all that it is not a rock would be a mineral.
So the dog is chasing its own tail.

[Mark Ost]

This is a really interesting topic and touches on scientific philosophy and systems of classification. There are many fields in science that experience the same problem. Linnean taxonomy works very well for present day organisms, but begins to have problems when you throw in the factor of time and evolution. There are mineraloids that do not fit the standard definition being composed of hydrocarbons or lacking the crystalline structure as defined by the standard definition. What to do? Ernst Mach realized that all scientific "laws" are of human construct only and are not to be given any more weight than that. Subject to change and rejection as needed. Though not perfect, these systems do give a foothold into justified belief and advance science but must be viewed non dogmatically.

As to the caves in Mexico, by being exposed to outside conditions, much formation may have stopped. Conditions in caves can go from depositional to solutional or back, for carbonate minerals by the variance of partial pressure of CO2 in the cave's atmosphere. I suspect temperatures are no longer conducive to further development. Caves are incredibly sensitive to any change in condition so are quite delicate.

[Vitaliy]

[kokoqn4o]

[Carles Millan]

[kokoqn4o]

[Carles Millan]

[marco campos-venuti]

Sorry kokoqn4o but synthetic rubies are not made with the same natural process and only have the same chemical composition but different structure. They are very easy to distinguish. Salt and halite are synonymous and are made at home or in lab with the same natural process, that is precipitation from a supersaturated solution. There is no way to distinguish.

[Vitaliy]

Kaloyan halite that is formed in conditions of a laboratory are no different from those that are formed from evaporate beds or from precipitation. The result is still Halite and as others have written it is almost impossible to distinguish each other. Therefore they are both considered natural even though one is made in outdoors conditions and the other is made in human/indoors/laboratory conditions.