A few questions about glass A glass, as I understand it, is a material whose solid phase is amorphous and which undergoes a glass transition when heated.  

My train of thought - and therefore my questions - began with obsidian.  My understanding is that obsidian is formed from material that would normally form crystalline rock, but since it's exposed to air during an eruption, it cools too rapidly to crystallize and therefore solidifies as glass.  This led me to wonder: how large can a lava stream be and still produce obsidian?  In particular, in season 7 of Game of Thrones, the island of Dragonstone is revealed to contain a veritable mountain of obsidian - is such a thing possible in the real world?  I would have thought that, above a certain volume, the center of the mass would be well-enough insulated so that crystallization could occur, spoiling the obsidian.  What's the largest mass of obsidian found in nature?

Thinking about too-rapid cooling led me to another question: can water form glass?  Is it possible to blast-freeze water so quickly that ice crystals do not form?  If so, what would be the properties of such a glass?

Finally, I wonder about regular, garden-variety silicate glass (as found in windows and bottles.)  Can it be cooled slowly enough so that crystals do form?  And if so, what are its properties?  (Have I essentially re-invented quartz?)
Q1: A volcano consists of many lava flows that occur over a long period of time.
In general, only very few of these lava flows have the right composition and  the right cooling history that are required to form obsidian.

This is why only parts of a volcano consist of obsidian, and by volume it's a generally a very small amount.

Q2: And yes there is amorphous ice. It is known since the 1980s. These days it is being used in laboratory environments, e.g. for electron cryomicroscopy. This is a high-tech-method for observing biochemical reactions and cellular processes in situ. The microorganisms need to be alive and in the middle of a reaction when shock-freezed. Researchers want to image atomic structures of the biomolecules, not from ubiquitous crystalline water so it better be amourphous.

Q3: Glass from windows and bottles contains more Na and K than most Granitic rocks. Na- and K-rich ingredients are being added as fluxing agent (limestone, soda), in the glass factory, decreasing the melting point of the silicates and therefore lowering the production costs.  

I think a melt of bottle glass, when crystallizing slowly would initially form the minerals Nepheline and Leucite, but late in the solidifcation process also Alkali Feldspar, and some Quarz, among other minerals. 

If you cooled it so slowly that no glass phase forms, you still might get zoned crystals, having with a different composition from core to rim. That depends on the absence/presence of impurities and local chemical (dis-) equilibria.