Mineral Factbook

Hydrotalcite

Mg6Al2(CO3)(OH)16(H2O)4IMA symbol: Htcapproved

Hydrotalcite is a carbonate or nitrate mineral with the formula Mg6Al2(CO3)(OH)16(H2O)4, crystallizing in the trigonal system. It has a Mohs hardness of 2, typically white in color, with a pearly luster, a specific gravity of 2.04-2.09. Its streak is brown.

Photos

Hydrotalcite specimen photo
Mai Seppel · CC BY-SA 4.0 · Commons
Hydrotalcite specimen photo
Shannon Heinle · CC0 · Commons
Hydrotalcite specimen photo
Robert M. Lavinsky · CC BY-SA 3.0 · Commons
Hydrotalcite specimen photo
Robert M. Lavinsky · CC BY-SA 3.0 · Commons

Crystallography

Crystal systemtrigonal crystal systemWikidata (CC0)
Space groupR -3 m :H
Cell (Å, °)a = 3.054, b = 3.054, c = 22.81; α = 90, β = 90, γ = 120
Cell volume184.244 ų, Z = 3
Axial ratios1.0000:1:7.4689calculated from COD 9009272
Source structureCOD 9009272 (Neues Jahrbuch fur Mineralogie, Monatshefte, 1969)

Powder X-ray diffraction (calculated)

2θ (degrees, Cu Kα1)I/I₀ (max 100)
d (Å)7.6031.9392.5763.8022.2881.527
I/I₀1003630.830.525.613.3

xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9009272; idealized occupancies, no preferred orientation.

Physical properties

Density (calculated)2.088 g/cm³calculated from COD 9009272
Hardness (Mohs)
2single sourceDana, System of Mineralogy, 6th ed. (1892)
Specific gravity
2.04-2.09 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892)
Color
whitesingle sourceDana, System of Mineralogy, 6th ed. (1892)
Streak
whitesingle sourceWikidata (CC0)
brownsingle sourceFord, Dana's Textbook of Mineralogy, 3rd ed. (1922)
Luster
pearlysingle sourceDana, System of Mineralogy, 6th ed. (1892)

Chemistry (calculated)

Molecular weight603.98 g/molcalculated from the IMA formula
Composition (wt%)Mg 24.14%, Al 8.93%, C 1.99%, O 60.93%, H 4.01%

Classification

Nickel-Strunz (10th)5.DA.50Wikidata (CC0)
Nickel-Strunz (9th)5.DA.50Wikidata (CC0)