Here we have another metal that is virtually unknown to all who walk this planet. Erbium is another member of the Rare Earths metal group. Occupying the top of the bottom two rows on the periodic table, they aren't all that rare in nature but they sure are so when it comes to finding them at your local hardware store. And yet this isn't entirely accurate. Most electronic devices have small amounts of various REs performing specialized functions because other elements can't do the job as well.... but talk about flying under the radar!

While the whole group behaves similarly at the molecular level, the REs have different characteristics. Some oxidize in air rapidly, some are soft while others are hard, you have heavy rare earth metals and there are light ones and so on.

Erbium flies under the radar even for the rare earth group. It has no record-breaking properties among its cousins. It is not especially reactive (can be kept indefinitely in open air without tarnishing), it is relatively heavy at 9g per cubic centimeter (but two others are heavier) and is slightly rarer than the average RE. Just about the only distinctive thing about Er is that its salts are colored a girly pinkish hue. Find expensive pink glassware and chances are that you're looking through a few billion atoms of our friend erbium :-)

Weight for the 10mm cube is 9.4±0.05g.