I always hear that Gemstones are created by means of extreme heat and pressure but I hear that Cristals/Quarz, are actually growing in Mountain caves, what amazes me is the shape of them, the sides seem to be completely plan and the edges absolutely straight, how come?
Are you wondering about quartz crystals?
Simple example: Suppose that you have a bunch of building blocks, and each individual building block is the same shape (let’s say a cube). And they have some tendency to stick together (maybe they’re magnetic, or have bumps and holes like Lego bricks, or whatever-- The details aren’t important). Now, you’ve got some sort of lump of a bunch of them stuck together, and you’re sticking more lumps on on the outside. The initial lump could be pretty much any shape, but you’ll find something interesting as you stick new blocks on. If you stick a new block on so that it’s only connecting on one surface, it won’t be a very strong connection, and is likely to be knocked off easily. But if you stick a new block on somewhere in a corner so that two or three surfaces of the block are connected, it’ll hold much better. Because of this effect, as you continually add new blocks onto your growing lump (and some fall off), the whole lump will tend to take on a cubical shape (or at least, some sort of boxy shape, even if the edges aren’t all the same length).
Now, then, each individual building block is an atom or molecule of whatever your crystal is made of. The shape of the individual building block reflects how those molecules tend to stick to other molecules (strictly speaking, it’s the shape of the crystal’s basic cell), and as a result of that, the whole crystal (the lump of blocks) tends to take on a regular shape. Cubes are the simplest example, but different shaped small blocks will lead to different sorts of overall crystal shape.
Yes, I was to lazy to check the spelling, sorry.
I think “Cronos” has covered it already but another question, why are they so important in electronic designs?
those so-called crystals growing in mountain caves aren’t quartz x’tals. they’re calcite (and sometimes other crystals like salt-halite.) these minerals could precipitate and re-crystalize at surface conditions.
quartz crystals form in undeground cavities (called vugs, cavities, fissures, etc.) the form from the walls of the cavity projecting towards the center. and you’re right, this occurrs at temperatures exceeding 500 degrees centgrd and at high pressure. quartz-filled fractures are called quartz veins and they often have gold deposits associated.
there are silicate deposits that could precipitate at surface conditions and chemically, they’re similar to quartz. chalcedony has a banded texture. not sure of the morphology of agate and other silicate deposits as i see them only as jewelry or decorative stones.
Precision cut quartz crystals are used to generate stable frequency references for one thing. They are extremely easy to build into an oscillator.
Would you mind to give a deeper explanation of how it’s done and why we need this oscillators,
I know that they are made artificially nowadays.
Thanks:)
In today’s world, most quartz crystals intended for us in electronic applications are grown in autoclaves under stringent conditions and controls; suffice it to say that the grown of the quartz crystal stones is not a trivial exercise.
The component that is usually referred to, in the electronics industry as a “crystal” is actually a little bit misleading; the proper name of such a component is a "piezoelectric quartz crystal unit.’ Their importance in the design of electronic oscillators boils down to the fact that they exhibit extremely high impedance at frequencies other than their design frequency; that impedance allows an oscillator to operate only at a frequency compatible with the design of the oscillator/ crystal combination. Manufacturing the little devils in not as easy as one might think
Much information is available at: http://www.ieee-uffc.org/frequency_control/index.asp I regret my inability properly present a link; but there it is.
Incidentally, piezoelectricity is a world all its own. If you have an interest in physics and/or crystallography in general, studying piezoelectricy is a worthwhile project.
You should be aware that you used to buy plug in crystal units for CBs and such. They didn’t all work at a single frequency.
I’ve noticed this before, you have an excellent way of describing things in a way that makes them understandable.
Of course they didn’t; quartz crystals can be made to operate at virtually any specific frequency you might require, up to slightly above 200.0 MHz; Its been almost fifteen years since I left the industry so they might now be available at frequencies greater than that mentioned. They can also be made at frequencies much less than 1.0 Mhz; if you have a modern electronic wristwatch it contains (most likely) a quartz crystal unit operating at 0.032768 MHz.
There are now ceramic “crystal” units as well, these days. Those are commonly found in remote controls and are resonate at a fairly low frequency. Those are referred to as ceramic resonators.
As for frequencies, I remember using 450 MHZ crystals years ago, but they’re probably being operated at a harmonic of a fundamental frequency.
BTW, Wikipedia has an excellent article on crystal oscillators. Crystal oscillator - Wikipedia
Ceramic resonators were readily available while I was still working in the frequency control industry. Calling them “resonators” was a stroke of marketing genius since anything that will resonate can be called a “resonator.” The plate of quarts inside a crystal unit is as much a “resonator” as is the piece of ceramic inside a “ceramic resonator.” The problem in frequency control with ceramic resonators is that their inherent “Q” value is much lower than in quartz, rendering them much less stable as a source of control. Plus, their behavior over extended temperature ranges is erratic.
The 450 MHz units you mention were in all probability operating on a high overtone. Are you sure they were were crystal units and not packaged crystal controlled oscillators?
There is a very specific “cut” of quartz that is named the “S/C” cut which showed a lot of potential for very high frequency operation; manufacturing them was very difficult but I would imagine most of those kinks have been worked out by now. They were coming in as I was leaving; it’s possible you had one of them.
That is an excellent article; someone put a lot of work into compiling that information. I had the pleasure of working with some of the people mentioned in the references-----not the Currie brothers; I’m not quite that old but I’m working on it.
As an aside, the regularity of a crystal structure is rather important in electronics, with respect to semiconductors. Silicon crystals form the same structure as diamonds (the gemstone, not a ‘diamond pattern’); adding imperfections to the structure is what allows there to be a way for charge carriers[sup]*[/sup] to move as in a conductor, under the right conditions.
Diamonds (Carbon crystals) can in fact be used as semiconductors as well - while it’s tougher to manufacture them for this purpose, they are terrific at thermal conductivity, a big limiting factor in current designs.
[sup]*[/sup]You can read this as ‘electrons’.