Prepare for ranting! And make it daunting! To protect the world from misinformation! To unite all facts within our lexicon! To defeat the evils of ignorance! To extend the reach of knowledge past happenstance! Me! Me! TVTMaster, ranting incoherently at the speed of light! Read this now, and know I'm right!
I've actually come up with a theory as to the origins and properties of rupees.
There are in fact three types of rupees, all of which take on a similar shape. Rupees are based largely off of a mineral substance found in much of the soil of Hyrule, traditionally referred to as Ruprose. Ruprose is a type of sugar, the crystals of which form a fourteen-sided polyhedron (the iconic rupee shape). This substance is found in many types of Hyrulean plants, due to its common occurrence in Hyrulean soil. Ruprose typically manifests into the Rupee crystal through three methods.
1- Ruprose-Glucose- Plant Rupees.
Many varieties of Hyrulean grasses use ruprose in much of their metabolism, along with glucose sugars. This mixture of sugars produces a sap which, although it has a high energy content when properly metabolized, is metabolized very slowly. As such, many grasses in Hyrule and adjoining lands have sap sacs, which burst when the grass is cut, releasing the ruprose. Upon exposure to oxygen, the Ruprose immediately crystallizes, with mature grasses producing rupees of adequate size to function as currency. These rupees typically look glossy and sticky, and are shorter and rounder than other types.
However, sunlight causes this type of rupee to quickly decompose and become worthless as currency. The ruprose and glucose is returned to the soil in raw form, allowing the remaining grass to quickly gain the energy to form new stalks. Many grasses also use ruprose in their cell walls, providing a stiffness that makes an adequate arrow shaft. Smaller, non-currency rupees can act as arrowheads, hence the spawns of arrows from cut grass. Some species even metabolize ruprose into an unstable form, that when not carefully stored can have explosive effects- hence bombs from grass. Hearts are typically explained separately- medicinal grasses produce a similar substance that seals wounds and encourages fibrin production.
2- Calcite Ruprose- Animal Rupees.
Because of the properties of ruprose in plants, many animals in Hyrule feed on said grasses. Ruprose cannot be easily metabolized by animals, therefore Hyrulean creatures, with rare non-ruprose plants to eat, found a way to use ruprose. Many creatures developed tough skins by allowing ruprose to crystallize in their skin, especially reptilian creatures. Most creatures, however, remove excess ruprose from their system with specialized organs that store ruprose. The enzyme that carries this sugar out of the bloodstream separates it from the glucose and bonds it to calcium-containing molecules, thus imparting a different quality to the rupee. While plant-produced rupee crystals are like hard candy and subject to melting, calcite rupees have a glassier, paler look, and don't melt like the glucose type. However, calcite rupees are quite fragile, as the calcium substances create gaps between ruprose crystals, which causes it to lose cohesion.
3- Mineral Ruprose- Rock Rupees.
Ruprose-rich soils that are eroded typically find their way into sedimentary rocks. While ruprose easily loses cohesion as a large crystal, it retains its properites even under extreme heat and pressure. Therefore, ruprose is often found in subterranean rock, which is frequently pushed to the surface by Hyrule's frequent seismic activity. While most rocks do not allow ruprose to gather in large enough quantities to form crystals, metamorphic and igneous ruprose geodes frequently form. Because ruprose's structure likes to form structures with other rupees, these geodes take a layer of rock with them. This structure also makes it difficult for rock to stay in cohesion with other rocks, meaning that ruprose geodes fall from cliff faces rather frequently. Large geodes contain other minerals that can affect ruprose's color, and when broken open contain a huge wealth of rare rupee colors. These geodes are typically fragile due to their hollow nature. However, while rock ruprose, with no other substance affecting its structure, is extremely durable, large concussive forces can compromise the stability of the crystal.
Whenever possible, rupees from animal and plant sources are refined into rock ruprose by boiling it. In water and heat, ruprose loses connection with other compounds, and floats to the top as a kind of green scum. This is filtered from the boiling water and impurities, and allowed to recrystallize into a normal rupee. Colored rupees are usually filtered separately with specific additives to prevent the separation of the ruprose from the color stain. Efforts to artifically infuse rupees with color have typically been failures.
So to sum- ruprose is a special sugar found in Hyrulean soil, readily crystallizes into rupees, and comes in different forms that must usually be refined before entering distribution.