| Mineral | HYDROMAGNESITE |
| Chemistry | Mg 5 [OH|(CO 3 ) 2 ] 2 · 4H 2 O |
| Transparency | crystals are transparent to translucent. |
| CrystalSystem | Monoclinic |
| CrystalHabits | include acicular, lathlike and platy crystals. Tiny spherical aggregates called puffballs are found attached to artinite crystals.A type of cave formation called bubbles which looks like white chewing gum bubbles are quite unique.Also found as concretions, encrustations and massive. |
| Fracture | perfect in one direction and distinct in another. |
| Hardness | 3½ |
| Characteristics | Fluorescent green in shortwave UV and bluish white in longwave UV light and crystals can be striated. |
| Occurences | include Alameda County; New Idria, San Benito County; Fresno County and other localities in California; Staten Island and Long Island, New York; Jewel Cave, South Dakota and the Grand Canyon, Arizona, USA; Soghan Mine, Kerman, Iran; Eastern Pyrenees, France; Mt. Vesuvius, Italy and British Columbia, Canada. |
| Indicators | crystal habits, associations, softness and density. |
| DensityNote | very light |
| IMAStatus | Approved |
| Discovered | 1827 |
| CellParameters | a = 10.11b = 8.94c = 8.38 β=114.58° |
| Ratio | a:b:c = 1.131 : 1 : 0.937 |
| OpticalType | Biaxial (+) |
| RI | n α =1.523 n β =1.527 n γ =1.545 |
| Birefringence | δ=0.022 |
| SurfaceRelief | Low |
| TypeLocality | Castle Point Hoboken Hudson Co. New Jersey U S A |
| Strunz | 5/E.01-10 5 : NitratesCarbonates & Borates E : Water-bearing carbonates with unfamiliar anions 01 : Hydromagnesite - Brugnatellite series |
