I’m very tired. Please help me understand this.
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It has to do with the composition of the sand (silica). Rocks tend to contain mainly quartz and feldspar.
You won’t be turning just any sand into glass. You certainly won’t be turning it into *clear* glass.
The ‘tiny rocks’ that can be made into glass are already transparent. Melting them together gets rid of voids and makes the bulk substance transparent.
Check out “How to Make Everything” on YouTube and search for “glass”. There are a few videos on the process of glass making, problems trying to make glass from scratch, etc.
What do you think sand is? It’s the result of those big rocks being crushed and abraded and sorted until what you have is rather pure quartz, because it’s much harder than the other minerals in the rock. We can do the same thing industrially, but there’s little point when there’s still plenty of glass-grade quartz left. Not to mention the huge amounts of waste that has no particularly productive use given the bulk.
both are possible but only the former is economically feasible i.e. we CAN turn big rocks into glass.
We can, it’s just a lot easier to control the process if we use lots of tiny rocks rather than one large one. To make glass that is useful (ie transparent and with the right properties), we need to use ingredients of exactly the right kind, and not all rocks, nor all sand, is suitable. It is easier with sand to make sure what you are putting into the mixture to make the glass is going to have the right composition to get the kind of glass you want out of it.
Rocks consist of lots of different minerals, most of which don’t make good glass. Sand consists mainly of quartz, which does make good glass. And not all sand will work: Glass makers need to find sand that’s almost pure quartz, and filter out the other stuff.
Sand is more than just “a bunch of tiny rocks”.
https://en.wikipedia.org/wiki/Sand#Composition
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 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.
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