THEORY #1: CASSANDRIUM IS AN UNDISCOVERED SUPERHEAVY ELEMENT

We’ve already discovered all the elements with atomic numbers from 1 to 118, and none of them have properties that exactly match Cassandrium. So what if it’s a REALLY new element with an even higher number? Once you get past uranium (element 92), all the elements we’ve found are highly unstable and will break down within a few seconds. However, scientists have theorized that some undiscovered elements might be part of an ‘island of stability’, where they have just the right nuclear configuration to be stable for a much longer time. And since we haven’t created any of these hypothetical elements yet... who knows, maybe one of them could look like Cassandrium.

This theory would also imply that Varian has somehow engineered a nuclear fusion reactor, which is pretty impressive but probably gave most of Corona radiation poisoning. Oops.

THEORY #2: CASSANDRIUM IS IODINE

Most elements that we know of are metals, but there is exactly one which is a purplish crystal at room temperature: iodine. Tangled is set in the 1780s (according to an interview with the creators), and iodine was discovered in 1811- so it’s very believable that no one in the setting would ever have seen it before.

However, iodine is also a toxic skin irritant, so... probably not a good idea to put it on a necklace.

THEORY #3: CASSANDRIUM IS A TRANSITION METAL

This is the most fun and believable theory in my opinion, but it relies on Varian having dramatized his explanation a little bit. Perhaps the pretty crystal (which we might call ‘Cassandrite’) is actually a glassy mineral similar to amethyst: silica quartz colored purple by trace impurities of a transition metal. (Transition metals are the elements in the center section of the periodic table.) This works with how Varian describes the workings of his ‘Elemental Remogrifier’:

In other words, the machine melts the sand (which is made of silica and trace deposits of other substances!) and then uses the pressure created by the rotational force to force it to solidify. (Slightly irrelevant side note: as a physics student I appreciate how Varian talks about counter-centrifugal force, i.e. what we would call centripetal force. Despite common misconception, centrifugal force does not technically exist!)

A pure silica crystal would be colorless, but Cassandrite is purple- which is presumably how Varian was able to realize that there was some kind of metal inside the mineral he created. That metal is the element which he names Cassandrium! This again fits with the scientific timeline, since many transition metals were not discovered until the 1800s.

Here’s where this concept gets really fun: transition metals can be mixed into steel to form new alloys which can be even stronger than regular steel. So if Cassandrium is actually a metal, and one day Varian discovers its applications in metallurgy...