eli5: Why does sand which is a bunch of tiny rocks, turn into glass, but we can’t turn big rocks into glass?

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I’m very tired. Please help me understand this.

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27 Answers

Anonymous 0 Comments

It’s because of the type of rocks sand is made of

Most Big rocks = a lot of different stuff

Sand = a lot of tiny silicate or quartz rocks

Anonymous 0 Comments

You can, it would just become a different type of glass. obsidian is considered to be a type of glass and slag from metal refining is also glass like or glass itself. It’s just to get specific properties it requires much more pure ingredients in specific proportions to ensure it has properties such as clarity, strength, colour, etc.

Anonymous 0 Comments

It’s specifically the silica in the sand that turns to glass. It’s not molten stone, it’s molten silica.

Anonymous 0 Comments

Sand is made of quartz (silica), a mineral. Not rocks.

Back to middle school science class my friend.

Anonymous 0 Comments

I kept reading Sandwich and was very confused about why the rest was talking about rocks and glass…..

Anonymous 0 Comments

The simple answer is that it can, except it has to be silica which most rocks arent fully composed of, and you need a lot more heat to do it.

Anonymous 0 Comments

Big rocks can in indeed be turned into glass with a generous application of the appropriate amount of mega-tonnage.

Anonymous 0 Comments

Most rocks are a mixture of aluminum and silicon oxides. Silicon oxide melts easily (which is why it makes good glass) but also breaks easily. Aluminum oxide is stronger but is more difficult to work with.

When rocks break down from wind and water, the soft silicon rich pieces get broken more easily into smaller pieces. The smaller lighter pieces get carried by wind and rivers while the bigger and heavier aluminum oxide rich pieces stay. The sand that is good for making glass is the sand that has been carried a long way from the mountain, and has a lot more silicon oxide grains.

So, back to your question. Before rocks can make good glass they need to be ground up and the hard/heavy parts taken out. Nature does this with wind and water.

Anonymous 0 Comments

sand is usually all quartz, rocks contain other stuff that hasn’t been withered away yet. you just want the quartz. but even if you had a pure quartzite rock, you’d rather take sand because just like how a big block of ice melts faster if you smash it apart, melting big rocks is a bother.

Anonymous 0 Comments

Can you flash melt a whole outcrop of rock and then quench it very quickly? Yes? Then you’ve got glass.

Practically, that is very hard to do due to the insane amount of energy required to melt a whole cliff of rock or whatever, then when you cool it it’s going to cool quickly on the outside and slowly on the inside, so that it crystallises beyond a few inches or so of the outer layer which would turn to glass.

The outer glass margin would not be a clear glass due to all the impurities in rock, it would be a dark colour (like obsidian). We often see this in rock which has been intruded by magma and then the magne body has just sat there cooling off until it crystallises. The magma body becomes igneous rock (Google ‘pluton’ to see what I mean) and the margins of both the igneous intrusion and the surrounding rock which was intruded into are often known as ‘chilled margins’ and are an inch or so of glassy material because it cooled off too quick to crystallise into a bunch of minerals.

You may also be interested in [fulgurites](https://en.wikipedia.org/wiki/Fulgurite) which are — poetically speaking — fossilised lightning strikes, or more literally they are the grains of quarts and silica rich minerals on a sandy beach that got struck by lightning, melted and fused together, then quickly cooled in a tube like structure which is made of glass. Its natural, so it’s somewhat messy and ugly compared to glassware or glass ornaments (which have been carefully crafted), but it’s definitely glass in the sense that it is an amorphous solid.