Calcium sulfate

Athanor · official

CaO₄S · 136.14 g/mol

Also called gypsum, plaster of Paris, E516

Inorganic

Open in Athanor

Drawn from its SMILES with RDKit

Names and identifiers

IUPAC name: calcium sulfate
Synonyms: gypsum, plaster of Paris, E516
+ 38 more
Anhydrous gypsum, Drierite, Karstenite, Muriacite, Basic calcium sulfate, Calcium sulfate, anhydrous, calcium sulphate, Calcium sulfate anhydrous, Crysalba, Osteoset, Thiolite, Anhydrous sulfate of lime, Natural anhydrite, Sulfuric acid, calcium salt (1:1), Anhydrous calcium sulfate, Oparex 10, GIBS, Franklin Fiber H 45, SSS-A, Calcium sulfate (1:1), Calcium sulfate (CaSO4), Calmatrix, Calcarea sulphurica 30C, CAS 20, Calcarea sulphurica, Dead-burned gypsum, Insoluble anhydrite, Raddichem 27, Denka sigma 1000, Shigao, Calcii sulfas, Stone paste, Calcium sulphate anhydrous, Anhydrous sulphate of lime, E934B3V59H, Shi gao, Sulfuric acid calcium salt (1:1), Calcium sulphate, anhydrous
Molecular formula: CaO₄S
Empirical formula: CaO₄S
Molecular weight: 136.14 g/mol
Exact mass: 135.91432
CAS number: 7778-18-9
PubChem CID: 24497
Canonical SMILES: [O-]S(=O)(=O)[O-].[Ca+2]
Isomeric SMILES: [O-]S(=O)(=O)[O-].[Ca+2]
InChI: InChI=1S/Ca.H2O4S/c;1-5(2,3)4/h;(H2,1,2,3,4)/q+2;/p-2
InChIKey: OSGAYBCDTDRGGQ-UHFFFAOYSA-L
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: For more Color/Form (Complete) data for CALCIUM SULFATE (7 total), please visit the HSDB record page.[6]
6 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– Calcium sulfate appears as odorless, white powder or colorless, crystalline solid. Crystals sometimes have a blue, gray or reddish tinge or can be brick red. Density: 2.96 g cm-3. [1] CAMEO Chemicals
– Large Crystals; Wet Solid; Liquid; Liquid; Other Solid; Dry Powder; Other Solid; Large Crystals; CBI; Dry Powder; Other Solid [2] EPA Chemical Data Reporting (CDR)
– WHITE HYGROSCOPIC POWDER OR CRYSTALLINE POWDER. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– Odorless, white powder or colorless, crystalline solid. [4] Occupational Safety and Health Administration (OSHA)
– Odorless, white powder or colorless, crystalline solid. [Note: May have blue, gray, or reddish tinge.] [5] The National Institute for Occupational Safety and Health (NIOSH)
–shown For more Color/Form (Complete) data for CALCIUM SULFATE (7 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
Odor: Odorless.[6]
2 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– PURE ANHYDROUS CALCIUM SULFATE IS ODORLESS [6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. and R.J. Lewis, Sr. (eds.). Hawley's Condensed Chemical Dictionary. 11th ed. New York: Van Nostrand Reinhold Co., 1987., p. 209
–shown Odorless. [6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 94-116. Washington, D.C.: U.S. Government Printing Office, June 1994., p. 48
Melting point: 1560 °C (2840 °F) (Decomposes) (NIOSH, 2024)[1]
3 values
3 of 3 sources agree on it (most common value).
Value As written Source
1560 °Cshown 2840 °F (Decomposes) (NIOSH, 2024) [1] CAMEO Chemicals
1560 °C 2840 °F (decomposes) [4] Occupational Safety and Health Administration (OSHA)
1560 °C 2840 °F (Decomposes) [5] The National Institute for Occupational Safety and Health (NIOSH)
Boiling point: Reported, but no value passed the checks.
The value and why
Decomposes (NIOSH, 2024) (could not be read; source [1])
Density: 2.96 (NIOSH, 2024) - Denser than water[1]
4 values
4 of 4 sources agree on it (most common value).
Value As written Source
–shown 2.96 (NIOSH, 2024) - Denser than water [1] CAMEO Chemicals
– 2.9 g/cm³ [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 2.96 [4] Occupational Safety and Health Administration (OSHA)
– 2.96 [5] The National Institute for Occupational Safety and Health (NIOSH)
Solubility in water: Solubility in water, g/100ml at 20 °C: 0.2 (very good)[3]
8 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– 0.3 % (NIOSH, 2024) [1] CAMEO Chemicals
– For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
– For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
– For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
– For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page. [6] Hazardous Substances Data Bank (HSDB)
– PURE ANHYDROUS SLIGHTLY SOL IN WATER [6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. and R.J. Lewis, Sr. (eds.). Hawley's Condensed Chemical Dictionary. 11th ed. New York: Van Nostrand Reinhold Co., 1987., p. 209
–shown Solubility in water, g/100ml at 20 °C: 0.2 (very good) [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 0.3% [5] The National Institute for Occupational Safety and Health (NIOSH)
Vapor pressure: Reported, but no value passed the checks.
The 3 values and why
0 mmHg (approx) (NIOSH, 2024) (no temperature given; source [1])
0 mmHg (approx) (no temperature given; source [4])
0 mmHg (approx) (no temperature given; source [5])

Value	As written	Source
–	Calcium sulfate appears as odorless, white powder or colorless, crystalline solid. Crystals sometimes have a blue, gray or reddish tinge or can be brick red. Density: 2.96 g cm-3.	[1] CAMEO Chemicals
–	Large Crystals; Wet Solid; Liquid; Liquid; Other Solid; Dry Powder; Other Solid; Large Crystals; CBI; Dry Powder; Other Solid	[2] EPA Chemical Data Reporting (CDR)
–	WHITE HYGROSCOPIC POWDER OR CRYSTALLINE POWDER.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	Odorless, white powder or colorless, crystalline solid.	[4] Occupational Safety and Health Administration (OSHA)
–	Odorless, white powder or colorless, crystalline solid. [Note: May have blue, gray, or reddish tinge.]	[5] The National Institute for Occupational Safety and Health (NIOSH)
–shown	For more Color/Form (Complete) data for CALCIUM SULFATE (7 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)

Value	As written	Source
–	PURE ANHYDROUS CALCIUM SULFATE IS ODORLESS	[6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. and R.J. Lewis, Sr. (eds.). Hawley's Condensed Chemical Dictionary. 11th ed. New York: Van Nostrand Reinhold Co., 1987., p. 209
–shown	Odorless.	[6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 94-116. Washington, D.C.: U.S. Government Printing Office, June 1994., p. 48

Value	As written	Source
1560 °Cshown	2840 °F (Decomposes) (NIOSH, 2024)	[1] CAMEO Chemicals
1560 °C	2840 °F (decomposes)	[4] Occupational Safety and Health Administration (OSHA)
1560 °C	2840 °F (Decomposes)	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–shown	2.96 (NIOSH, 2024) - Denser than water	[1] CAMEO Chemicals
–	2.9 g/cm³	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	2.96	[4] Occupational Safety and Health Administration (OSHA)
–	2.96	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	0.3 % (NIOSH, 2024)	[1] CAMEO Chemicals
–	For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)
–	For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)
–	For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)
–	For more Solubility (Complete) data for CALCIUM SULFATE (6 total), please visit the HSDB record page.	[6] Hazardous Substances Data Bank (HSDB)
–	PURE ANHYDROUS SLIGHTLY SOL IN WATER	[6] Hazardous Substances Data Bank (HSDB)cites Sax, N.I. and R.J. Lewis, Sr. (eds.). Hawley's Condensed Chemical Dictionary. 11th ed. New York: Van Nostrand Reinhold Co., 1987., p. 209
–shown	Solubility in water, g/100ml at 20 °C: 0.2 (very good)	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	0.3%	[5] The National Institute for Occupational Safety and Health (NIOSH)

Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.

Calculated

Heavy atoms: 6
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0
H-bond donors: 0
H-bond acceptors: 4
Rotatable bonds: 0
TPSA (Å²): 80.3 computed here · PubChem 88.6
Formal charge: 0
Complexity: 62 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: Td of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

Ca29.44%
O47.01%
S23.55%

Isotope pattern

Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.

Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.

Predicted

log P: -1.72 Crippen (Wildman and Crippen 1999)
log S (water solubility): 0.4 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 4.18 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 136.14
log P ≤ 5 (Crippen): -1.72
H-bond donors ≤ 5: 0
H-bond acceptors ≤ 10: 4

Passes all four rules.

Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.

Safety

This chemical does not meet GHS hazard criteria for 93.5% (1291 of 1381) of all reports.[7]

Exposure limits

PEL-TWA (8-Hour Time Weighted Average): 15 mg/m³ (total dust), 5 mg/m³ (respirable fraction)[4]
PEL: TWA 15 mg/m3 (total) TWA 5 mg/m3 (resp)[5]
REL-TWA (Time Weighted Average): 10 mg/m³ (total dust), 5 mg/m³ (respirable fraction)[4]
REL: TWA 10 mg/m3 (total) TWA 5 mg/m3 (resp)[5]
TLV: (inhalable fraction): 10 mg/m[3]
IDLH: N.D. See: IDLH index[5]

First aid

Excerpt from NIOSH Pocket Guide for Calcium sulfate: Eye: Irrigate immediately - If this chemical contacts the eyes, immediately wash (irrigate) the eyes with large amounts of water, occasionally lifting the lower and upper lids. Get medical attention immediately. Skin: SOAP WASH - If this chemical contacts the skin, wash the contaminated skin with soap and water. Breathing: Fresh AIR - If a person breathes large amounts of this chemical, move the exposed person to fresh air at once. Other measures are usually unnecessary. (NIOSH, 2024)[1]
(General first aid procedures) Eye: Irrigate immediately - If this chemical contacts the eyes, immediately wash (irrigate) the eyes with large amounts of water, occasionally lifting the lower and upper lids. Get medical attention immediately. Skin: Soap wash - If this chemical contacts the skin, wash the contaminated skin with soap and water. Breathing: Fresh air[5]
Fresh air, rest.[3]
Rinse and then wash skin with water and soap.[3]

Storage

Dry.[3]
KEEP DRY. (dihydrate)[6]

Incompatibilities

Many metal oxo-compounds (nitrates, oxides and particularly sulfates) and sulfides are reduced violently or explosively (ie undergo 'thermite' reaction) on heating an intimate mixture with aluminum powder to a suitably high temperature to initiate the reaction. (sulfates, including calcium sulfate)[6]
Contact of diazomethane vapor and (calcium) sulfate causes an exotherm which may lead to detonation.[6]
Excess red phosphorus will burn admixed with barium or calcium sulfates if primed at a high temperature with potassium nitrate-calcium silicide mixture.[6]
Diazomethane, aluminum, phosphorus, water [Note: Hygroscopic (i.e., absorbs moisture from the air). Reacts with water to form Gypsum & Plaster of Paris].[6]

Safety data sheets on the supplier’s page: Alfa Chemistry, Angene Chemical, Clinivex.

Always read the supplier’s safety data sheet before working with it.

Spectra

Other MSHazardous Substances Data Bank (HSDB)
FTIRSpectraBase (KBr WAFER)
ATR-IRSpectraBase (Bio-Rad FTS · ATR-Neat (DuraSamplIR II))
RamanRRUFF Project · RRUFF Project · RRUFF Project · RRUFF Project · RRUFF Project · RRUFF Project

Experimental spectra held by these sources; each link opens the source's own record.

Literature

Reading PubChem, OpenAlex and GSRS…

Bioactivity

Reading ChEMBL…

References

[1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
[2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
[3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
[4]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
[5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
[6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[7]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[8]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[9]RRUFF Project · Linked only · via PubChem · retrieved 2026-10-14
·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
·Literature on PubChem

Data last updated 2026-10-14.