Barium sulfate

Ba 1
S 1
O 4

Formula unit Lattice

Choose Lattice to see eight unit cells. Then drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

6 atoms in one formula unit of an ionic lattice.

The drawing shows one formula unit of an ionic lattice, not a molecule; barium sulfate has no molecular shape.

IUPAC name: barium(2+) sulfate
Molar mass: 233.386(34) g/mol
Atoms: 6
SMILES: [O-]S(=O)(=O)[O-].[Ba+2]
InChIKey: TZCXTZWJZNENPQ-UHFFFAOYSA-L
PubChem CID: 24414

Made of

Ba S O

Mineralogists know barium sulfate as barite; in commerce it sometimes goes by barytes, and the Hazardous Substances Data Bank (HSDB) records the name heavy spar as well. Natural barite carries impurities, which HSDB names as iron(III) oxide, silicon dioxide and strontium sulfate. The US National Cancer Institute’s NCI Thesaurus calls the compound the sulfate salt of barium, a divalent metal, meaning one whose ions carry two positive charges. The IUPAC name, barium(2+) sulfate, writes that charge in.

Sulfur and oxygen make up the sulfate ion, and the molar mass is 233.39 g/mol. CAMEO Chemicals, a US hazards database, describes a white or faintly yellow powder or small crystals with no smell. Its uses, as HSDB lists them, run from weighting oil-drilling mud to paper coatings, paints, plastics and lithograph inks. In textiles it acts as a filler and as a delustrant, which dulls a fibre’s shine.

Structure and bonding

The formula-unit drawing shows a barium ion, Ba²⁺, and a sulfate ion, SO₄²⁻, as two unconnected pieces. In the drawing, the sulfur atom is joined to four oxygen atoms, by double bonds to two and single bonds to the other two. The drawing gives each singly bonded oxygen a charge of −1. The two ions together are one formula unit, the lattice’s ratio of ions written out once, not a free-standing particle. The ion’s measured bond lengths are on the calcium sulfate page.

Eight unit cells fill the Lattice view, each outlined and each the crystal’s smallest repeating box of ions. One cell holds four barium ions and four sulfate ions. A single cell is too small to hold any ion’s full set of neighbours, which the block of eight provides. Coordination picks out one barium ion and its 12 nearest oxygen atoms, 2.77 to 3.31 Å away, in seven different sulfate ions. Twelve oxygen atoms from seven ions means that some of those sulfate ions offer it two each.

HSDB describes the solid as white orthorhombic crystals with a hardness of 3.3 on the Mohs scale, which ranks minerals by what they can scratch.

Where it turns up

China, India and Morocco, the three leading barite producers, were also the world’s leading exporters of it, according to the US Geological Survey’s 2022 Minerals Yearbook. Barite also goes into brake and clutch pads and automobile paint primer, the Survey reports, and barite-filled materials have quietened engine compartments in cars, boats and trucks. It is also used in the cement jacket around oil pipelines laid under water. Los Alamos adds paint, where the sulfate serves as the pigment permanent white, and glassmaking.

Lipstick is one of the cosmetics in which HSDB lists barium sulfate as a filler. The Cosmetic Ingredient Review Expert Panel found it safe as cosmetics now use it and at their present concentrations, if the product is formulated to be non-irritating.

Why it matters

Drilling fluid typically takes about 70 per cent of world barite consumption, according to the US Geological Survey’s 2022 Minerals Yearbook. Because drilling is its main use, ground-barite sales have generally tracked the count of active rigs. In 1985 drilling fluids took over 65 per cent of barite output, and in 1986 demand fell by half, chiefly through a slump in drilling, according to HSDB.

Barium in a sample can be measured by precipitating it as the sulfate, bringing it out of solution as a solid. Such precipitation leaves almost none of one or both ions behind. Gravimetric analysis of this kind, measurement by weighing, was long a mainstay of chemical analysis before instrumental methods largely replaced it, according to Chem1.

In medicine, the NCI Thesaurus describes barium sulfate as a radiopaque agent, opaque to X-rays, for diagnosing gastrointestinal conditions. For years it was sold in the United States as an unapproved drug. The first barium sulfate product won approval from the Food and Drug Administration on 11 January 2016.

Properties

Properties of barium sulfate Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 24414.
Property	Value	Unit	Source
Formula (Hill order)	BaO₄S
Molar mass	233.386(34) g/mol	g/mol	IUPAC/CIAAW 2024
Barium atoms	1
Sulfur atoms	1
Oxygen atoms	4
PubChem molecular weight	233.39 g/mol	g/mol	PubChem

Safety

In its everyday forms barium sulfate is a low hazard, non-toxic in CAMEO Chemicals’ words, though HSDB warns that soluble impurities can cause toxic reactions. Its dust is the exception: NIOSH, the US institute researching workplace safety and health, lists baritosis, a benign dust disease of the lungs, among the effects of breathing it. Japan’s national classification adds damage to the respiratory organs through repeated exposure. NIOSH and OSHA, the US workplace regulator, set limits for the dust, recorded on the NIOSH Pocket Guide card, while the PubChem Laboratory Chemical Safety Summary brings its hazards together.

Questions

Is barium sulfate soluble in water?

Barely. HSDB gives a solubility of 0.00031 g in 100 g of water at 20 °C, and it does not dissolve in ethanol. Dilute acids leave it undissolved too, CAMEO Chemicals adds, though hot concentrated sulfuric acid takes it up. Chloride and other negative ions in the water raise its solubility markedly, according to HSDB. No such figure can be predicted in advance: too many variables govern how far any salt dissolves (Chem1).

What are lithopone and blanc fixe?

Both are white pigments based on barium sulfate. Blanc fixe is the precipitated compound, made, HSDB says, by mixing water solutions of barium sulfide and sodium sulfate. Lithopone combines barium sulfate with zinc sulfide. Los Alamos credits lithopone with good covering power and says it does not darken when sulfides are present, and HSDB records its wide use in white paints.

Why is barite used in drilling mud?

Barite is a weighting agent, a dense solid added to the fluids used in drilling oil and gas wells; HSDB gives barium sulfate a density of 4.49 g/cm³. According to the US Geological Survey's 2022 Minerals Yearbook, barite's advantages there are its high specific gravity, density measured against water's, and low abrasion. Others are chemical and physical inertness, low oil absorption, low solubility and nontoxicity.

Is barium sulfate harmful to the environment?

It is not a listed toxic chemical under Section 313 of EPCRA, a 1986 US right-to-know law, because it is very insoluble, according to the US Geological Survey. Dissolved barium from soluble compounds soon combines with sulfate or carbonate in natural water, ending up in those longer-lasting forms, according to the US Agency for Toxic Substances and Disease Registry. Japan's national classification, however, rates barium sulfate as harmful to aquatic life, with effects that persist.