# crystal vs. glass **URL:** \ **Category:** Factual Questions\ **Created:** [September 16, 1999, 3:27am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363 "1999-09-16T03:27:00Z")\ **Posts on this page:** 7\ **Page:** 2
**Author:** ![mikan](https://avatars.discourse-cdn.com/v4/letter/m/cc9497/32.png) [@mikan](https://boards.straightdope.com/u/mikan)\ **Post date:** [September 18, 1999, 5:17am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/21 "1999-09-18T05:17:00Z")
Yikes. I think I’m going to stay away from antique stores until I forget about that last tidbit. ---
**Author:** ![Doobieous](https://avatars.discourse-cdn.com/v4/letter/d/da6949/32.png) [@Doobieous](https://boards.straightdope.com/u/Doobieous)\ **Post date:** [September 18, 1999, 5:50am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/22 "1999-09-18T05:50:00Z")
I’ve seen a pure sample of silicon that was used when they create microchips (it looked kind of like a top). It was dark gray and silvery in color. Quite light for its size. When I saw it at the front of the class on one of the desks I thought it was a chunk of lead. My Chem teacher obtained it from one of the other professors just to show us (she was THE coolest chem teacher, but I digress) I have also seen a quartz “glass” tube . It looked a lot like glass except the cut ends were clear (a comparable glass tube had the typical greenish end). I’m wondering, if this tube of quartz tube were to break, would it break along a plane, or would it break into rounded pieces like the glass tube? ---
**Author:** ![CatInHat](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@CatInHat](https://boards.straightdope.com/u/CatInHat)\ **Post date:** [September 21, 1999, 5:39am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/23 "1999-09-21T05:39:00Z")
IIRC (from a tour of the Steuben workshop in Corning a few years back), leaded crystal is softer than regular glass. That’s why it can be cut. Of course, it’s not soft enough to be able to tell the difference just by touching it; it’s still pretty hard. * * * The Cat In The Hat ---
**Author:** ![bill422](https://avatars.discourse-cdn.com/v4/letter/b/eb9ed0/32.png) [@bill422](https://boards.straightdope.com/u/bill422)\ **Post date:** [September 20, 1999, 11:41pm UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/24 "1999-09-20T23:41:00Z")
A few more points about silicon and quartz. This is what I’ve picked up, since my research deals directly with putting chemicals on silicon using UV light that passes through a quartz window. (Is this relevant or what?). Quartz is nothing more than very pure glass. They both are made of silicon dioxide. Quartz, being pure, allows UV light to pass through. The impurities in ordinary glass don’t allow UV light to pass. When quartz is broken it breaks like glass, no crystal structures–just shattered glass. (trust me, I have personal experience involving a $200 piece of quartz–SHIIIIIIIT!!!). Pure silicon, in the electronics trade IS crystaline, similar to diamond (don’t confuse pure silicon with quartz or glass which is silicon dioxide). Moreover, the silicon can be polished on one crystal face or another, or even diagonally to produce even more types of faces (these different faces go by names like silicon (111), silicon (001) or silicon (110). The silicon used almost exclusively in computer chips is Si (001). ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [September 21, 1999, 1:58am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/25 "1999-09-21T01:58:00Z")
> [@](#): > > The impurities in ordinary glass don’t allow UV light to pass. > -Bill The sunburned right arm I acquired while a passenger in a van driving eastward across Texas would question this assertion. If glass filters out all UV light why do we special (polarized IIRC) sunglasses for driving? * * * Sue from El Paso [members.aol.com/majormd/index.html](http://members.aol.com/majormd/index.html) ---
**Author:** ![bill422](https://avatars.discourse-cdn.com/v4/letter/b/eb9ed0/32.png) [@bill422](https://boards.straightdope.com/u/bill422)\ **Post date:** [September 21, 1999, 11:34am UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/26 "1999-09-21T11:34:00Z")
Okay Fine! Let me amend that. The impurities in glass keep enough UV light from passing through that science types have to buy expensive quartz glass to do real UV work. ---
**Author:** ![torq](https://avatars.discourse-cdn.com/v4/letter/t/dfb087/32.png) [@torq](https://boards.straightdope.com/u/torq)\ **Post date:** [September 21, 1999, 6:32pm UTC](https://boards.straightdope.com/t/crystal-vs-glass/3363/27 "1999-09-21T18:32:00Z")
> [@](#): > > why do we special (polarized IIRC) sunglasses for driving? Polarized glasses are good for reducing the light reflected from shiny surfaces (like the rear window of the car in front of you, or the snow and ice covering the ground during winter in less fortunate climes, or bodies of water). To the best of my knowledge, polarized filters don’t do anything in particular to UV light which they don’t also do to visible light. [Previous page](https://boards.straightdope.com/t/crystal-vs-glass/3363.md?page=1)