I’m very tired. Please help me understand this.
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You could, it’s just not efficient to do so… think of how quickly a handful of snow would melt indoors vs. a solid block of ice that fits in your hand. Same idea for turning sand to glass vs. larger rocks.
This is mainly because sand is _not_ just a bunch of tiny rocks. Your initial premise is flawed. There’s tiny rocks in sand, but that’s only a small portion of what sand is.
In general you can.
It just doesn’t make very nice or useful glass as most big rocks are made of the wrong stuff.
And the big rocks made of the right stuff to give us good glass are harder to melt and deal with due to size. So it’s easier to use the tiny rocks of the good stuff in the right type of sand than to try using bigger rocks.
Well, strictly speaking, you CAN turn a rock into glass, but the rock is made of many different minerals which each have their own particularly melting/freezing/crystallization temps that makes the solution (which is what a magma is, a solution in a SiO2-dominant liquid). Using quartz gives a fairly pure solution (SiO2 liquid) which tends to not have the many crystal formation and inhomogeneity problems that happen from very impure liquids. Also, quartz is transparent to visible light so useful as glass.
It is like trying to freeze salty water compared to pure water. The secondary materials cause lots of problems for making whatever the person wants. A little sodium borate is nice as an additive, say, or a bit of lead, which can help lower melting temps and make the glass easier to work with (pure silica glass is a real bear to work with, very viscous and has to be really hot because quartz/SiO2 has a very high melting temperature).
In effect, all magma, lava, is melted rock, and if you look around at what happens in nature, you will find that most of that melted stuff does no make a nice and useful glass. All those other elements muck up the works, so to speak.
Like melting different sized ice cubes- different sizes melt at different rates, and smaller pieces melt faster, because 100rams of tiny ice cubes has a lot more surface area than a solid cube of 100g of ice. (Which is why ice spheres are popular in whiskey drinking-they have the least surface area and melt the slowest).
A regular kiln for making ceramics (sand-sized pieces of rocks+minerals, that are melted together to fuse them) top out around 2400f/1300c. As many have pointed out, quartz mineral is almost all silica- which is the primary mineral for glass. Quartz melts at about about 3,000f/1670c. And we probably have industrial kilns that can do that temp.
So- like melting a big piece of ice- it would talk more energy for more time to melt a big piece of quartz into liquid than it would to throw that quartz into a grinder, to make a powder with LOTS of surface area, and turn that into the same liquid to pour.
“Big rocks” like iron? We melt “Big rocks” into iron, not glass.
The two most common minerals on earth are quartz and feldspar. Granite is a mix of those two with a few other things added, and many other rock types are the result of those mineral being mixed and re-combined with heat and pressure.
Feldspar is actually a family of minerals, but what you get if you heat it to melting is basically porcelain, rather than glass.
When weather breaks rock down over the course of many years, it separates the quartz and feldspar, because of the difference in particle size and weight. Sand is mostly quartz, and clay is mostly feldspar. We make lots of things by heating clay, just like we heat glass, but a mix of the two isn’t really good.
Glass is only about 70% silica, the rest is lime and a mineral called soda ash, which is somewhat similar to fireplace ash. Pure quartz glass is used for some purposes, but it is difficult to work with and requires much higher temperatures to make.
Sand isn’t just tiny rocks; it is specifically silica. “Why would a bunch of silica remain as sand? Why isn’t it all in giant crystals of quartz (which is made of silica)?” is a good follow-up question. Here is a slightly over-simplified explanation, but it should suffice for ELI5.
Highly composite rocks usually have a huge mix of mineral types, and they all have different ways of weathering (breaking down chemically, especially with exposure to cycles of hot and cold, moist and dry). All the stuff that can dissolve away goes first; that includes sodium, potassium, lithium, etc. (That’s one of the reasons the sea is salty; all the salt dissolves out of land rocks and flows to the oceans where it has been accumulating since earth first formed oceans.) Phorphorous bearing minerals also gradually get taken away, whether by biological action of things like fungi, or by weathering. The rest of the stuff tends to decompose into clay particles, and washes away. Since silica is what glass is made of, and glass is essentially inert (with a few rare exceptions of potent acids that can react with silica), rocks that have a big mix of quartz and mica and other stuff (such as granite) end up as a porous bunch of crumbling rock that’s mostly silica. You may have seen crumbling weathered granite if you ever hike to any place with exposed granite in the mountains. Most of the crumbly stuff that remains is silica/quartz. As it actually crumbles into rubble, more of the stuff that can weather away does weather away. This crumbled mostly silica stuff, if it is near the ocean where physical bashing of the waves can really grind it up, crumbles further and breaks down into the smallest particles that waves will grind it into over long periods of time. The weathering of minerals when in contact with pounding waves of salt water is also accelerated, but since silica is essentially inert, only it remains. But sea water isn’t the only thing that will make sand. Any rock which has silica mixed in with other minerals that will eventually weather away will leave you with sand, especially if there is some kind of abrasion or physical impact to help it along.
That’s how silica sand is made.
BTW, Beach sand often has a lot of tiny mollusk shells and tiny bits of broken larger mollusk shells, so beach sand isn’t always pure silica.
Yes we can and do. This is how Rockwool is made. But only specific rock/sand will be made into clear glass. So process is much better with small particles aka sand.
Sand is more than just “a bunch of tiny rocks”.
https://en.wikipedia.org/wiki/Sand#Composition
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