Why do people use stone or metal cubes rather than ice, and why not frozen alcohol?

The physics of why ethanol cubes are impractical is decisive: its freezing point is around minus 114 degrees Celsius.

That is far colder than a domestic freezer, colder than dry ice, and reaching it requires specialised equipment. So pure alcohol cubes are not something anyone is making at home.

A cube of a mixture — a spirit, which is mostly water — freezes at a temperature that depends on its strength. A typical spirit at forty percent will freeze somewhere around minus 27 degrees, which most domestic freezers cannot reach. Weaker mixtures freeze higher and are achievable.

And if you did have very cold alcohol, handling it would be genuinely hazardous — liquid at that temperature causes serious cold injury on contact, and it does not feel cold in the way ice does until damage is done.

The more interesting point is the one hiding in your comparison of materials: most of ice's cooling power comes from melting, not from being cold.

Melting a gram of ice absorbs about eighty times the energy that warming a gram of water by one degree does. That latent heat is the whole reason ice works so well.

So a stone or metal cube, which only warms up and never melts, can absorb only a small fraction of what an equivalent piece of ice can. They keep a drink cool for a short time and cannot chill a room-temperature drink meaningfully. People who use them are choosing no dilution over actual cooling, and often do not realise how large that trade is.

A frozen spirit cube has the same limitation. It would melt, but a much smaller share of it and at a much lower latent heat, so the cooling is far weaker than water ice.

Which means the dilemma is real: dilution and cooling come from the same physical process, and you cannot have one without the other.

The practical answers people actually use, given that trade:

Chill everything beforehand. The glass, the bottle, the mixers. A drink assembled from cold components needs almost no cooling in the glass.

Use large cubes or spheres. Less surface area per unit of mass means slower melting, so you get a longer period of cooling with less dilution over the time you actually drink it. This is why bars use big cubes for spirits.

Freeze the mixer. Cubes of tonic, juice or coffee dilute the drink with more of itself rather than with water. This is a genuinely good technique for iced coffee in particular.

Accept some dilution. For many spirits a little water is not a fault — it is why people add a few drops deliberately. The objection to ice is usually about too much dilution over time, not about any.

Worth adding that stone and steel cubes have a hygiene consideration people forget: they go from a drink back into a freezer and get reused, often with a rinse rather than a wash.

Ice is used once. Reusable cubes need washing properly between uses, and the porous stone ones in particular can hold residue. Not a reason to avoid them, and a reason to treat them as utensils rather than as ice.