I have compiled a list of sources for the elements that are available to the amateur chemist. Tantalum will be discussed here.
Tantalum is an extremely dense, bluish-gray metal. It is named after the king Tantalus, who was submerged in water he could not ever drink and was near fruit he could never eat. Tantalum's behavior of being submerged in acids but never able to dissolve was the reason that it was given the name. Tantalum is a rare and expensive metal, found in niobium ores. It was mistakenly confused with niobium, despite its much higher density, and is difficult to remove from the aforementioned metal. When tantalum is pure, it has excellent physical strength and properties, making it ideal for artificial limbs and fine medical instruments. Tantalum, despite its seeming invincibility, has its weak points; it can be dissolved in hydrofluoric acid or molten hydroxides. Tantalum is primarily pentavalent, which is part of the reason for its inertness. The oxide is a white unreactive substance, difficult to reduce to the metal. It can be made to form compounds to dissolving in molten metal hydroxides or electric arc fusion with other metals, forming a range of tantalates.
In element form: High capacity (30 mfd or so) tantalum capacitors have a lump of anodized tantalum in the middle. Use hot hydrochloric acid to dissolve any manganese dioxide which may be present. Some expensive medical instruments use tantalum.
In compound form: Motion sensors may contain lithium tantalate as the sensing material.
Here is my sample of tantalum. It is a nugget of tantalum metal with tantalum connector wire, taken from a 22 mfd tantalum capacitor. The green anodized color is visible in certain places.