| Greenlizardite | |
| Category: | Sulfate |
| Formula: | (NH)4Na(UO2)2(SO4)2(OH)2•4H2O |
| Imasymbol: | Glz[1] |
| System: | Triclinic |
| Symmetry: | P |
| Unit Cell: | a = 6.83617 Å, b = 9.5127 Å c = 13.8979 Å; α = 98.636°, β = 93.713°, γ = 110.102°; Z = 2 |
| Color: | Light green-yellow |
| Habit: | Bladed |
| Cleavage: | Perfect along and good along |
| Tenacity: | Brittle |
| Mohs: | ~2 |
| Luster: | Vitreous |
| Refractive: | nα= 1.559 nβ= 1.582 nγ= 1.608 |
| Opticalprop: | Biaxial positive |
| Birefringence: | δ = 0.049 |
| Pleochroism: | Weak |
| Density: | 3.469 g/cm3 (calculated) |
| Diaphaneity: | Transparent |
| Other: | Radioactive |
Greenlizardite is a rare sulfate mineral discovered underground in the Green Lizard Mine, which the mineral was named for, in Utah. The mineral was found in mineralized ore channels within the Shinarump member of the Chinle formation. It occurs as a secondary alteration phase. It is associated with ammoniozippeite, boussingaultite, and dickite. Greenlizardite was approved as a mineral by the International Mineralogical Association in 2017.[2]
Greenlizardite forms in a bladed habit, with blades up to 0.3 mm long. Its color is light green-yellow. It is highly soluble in water at room temperature. Its hardness is approximately two on the Mohs hardness scale and it has a white streak. Greenlizardite is brittle with irregular fracture. It has perfect cleavage in the [001] direction and good cleavage in the [2{{overline|1}}0] direction. It is transparent and has vitreous luster. The calculated density of the empirical formula of Greenlizardite is 3.469 g/cm3.
Greenlizardite is biaxial positive. Twinning is observed in cross polarized light and it displays weak pleochroism and moderate dispersion. Under a 50 mW 540 nm blue violet laser, it fluoresces greenish-blue. Refractive indices are α = 1.559, β = 1.582 and γ = 1.608.[2]
The calculated empirical formula of Greenlizardite is (NH4)0.98Na1.00U1.96S2.04O18.00H10.0. Its ideal formula is (NH4)Na(UO2)2(SO4)2(OH)2·4H2O.
A U6+ atom is surrounded by 7 O atoms in a pentagonal bipyramid shape. These UO7 pentagonal bipyramids are connected in pairs, sharing one common edge. The UO7 dimers share corners with SO4 groups, forming sheets with the composition [(UO<sub>2</sub>)<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>]2- . These sheets are parallel to the (001) plane. The corner of each SO4 group not shared with the UO7 bipyramids within the same sheet points in the same direction. Each Na atom is bonded to two different uranyl O atoms in two separate adjacent sheets. Each Na atom is also bonded to two Sulfate O atoms from each of the two adjacent sheets, for a total of 6 O atoms coordinated around. These NaO6 octahedra are oriented along the (100) plane in zigzag shaped chains by sharing edges. These zigzag shaped chains link the two adjacent sheets together to form a slab. Within this slab structure, there are channels along the (100) plane that contain isolated H20 groups. The slabs are connected by a NH4 bonded to two uranyl O atoms from one adjacent slab and one equatorial O atom from a UO7 group in the other slab, as well as three H2O groups.