When isolated, holmium is relatively stable in dry air at room temperature.

It is a relatively rare lanthanide, making up 1.4 parts per million of the Earth's crust, an abundance similar to tungsten.

Its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho(III) ions.

With a boiling point of 3,000 K (2,727 °C; 4,940 °F), holmium is the sixth most volatile lanthanide after ytterbium, europium, samarium, thulium and dysprosium.

At standard temperature and pressure, holmium, like many of the second half of the lanthanides, normally assumes a hexagonally close-packed (hcp) structure.

[15] Holmium metal tarnishes slowly in air, forming a yellowish oxide layer that has an appearance similar to that of iron rust.

It burns readily to form holmium(III) oxide:[16] It is a relatively soft and malleable element that is fairly corrosion-resistant and chemically stable in dry air at standard temperature and pressure.

[17] In pure form, holmium possesses a metallic, bright silvery luster.

[26] The high excitation energy, resulting in a particularly rich spectrum of decay gamma rays produced when the metastable state de-excites, makes this isotope useful as a means for calibrating gamma ray spectrometers.

[28] The color change is related to the sharp emission lines of trivalent holmium ions acting as red phosphors.

[30] Under high pressure, holmium(III) sulfide can form in the cubic and orthorhombic crystal systems.

[37] Organoholmium compounds are very similar to those of the other lanthanides, as they all share an inability to undergo π backbonding.

They are thus mostly restricted to the mostly ionic cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.

[38] Holmium (Holmia, Latin name for Stockholm) was discovered by the Swiss chemists Jacques-Louis Soret and Marc Delafontaine in 1878 who noticed the aberrant spectrographic emission spectrum of the then-unknown element (they called it "Element X").

[39][40] The Swedish chemist Per Teodor Cleve also independently discovered the element while he was working on erbia earth (erbium oxide).

[8][7][41] Using the method developed by the Swedish chemist Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia.

[42] In the English physicist Henry Moseley's classic paper on atomic numbers, holmium was assigned the value 66.

He would have seen x-ray emission lines for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity.

The main mining areas are China, United States, Brazil, India, Sri Lanka, and Australia with reserves of holmium estimated as 400,000 tonnes.

Holmium-doped yttrium iron garnet (YIG) and yttrium lithium fluoride have applications in solid-state lasers, and Ho-YIG has applications in optical isolators and in microwave equipment (e.g., YIG spheres).

[57] In March 2017, IBM announced that they had developed a technique to store one bit of data on a single holmium atom set on a bed of magnesium oxide.

[59] Holmium is used in the medical field, particularly in laser surgery for procedures such as kidney stone removal and prostate treatment, due to its precision and minimal tissue damage.

[65][66][67] Large amounts of holmium salts can cause severe damage if inhaled, consumed orally, or injected.