Lautenthalite is a mineral that was named after its location, Lautenthal, Harz mountains, Germany. It can be found in several slag localities. It was approved by the IMA in 1993. It is a member of the devilline group, and it is the lead analogue of devilline and campigliaite. Without analytical methods, it is hard to distinguish the mineral from both. It shows pleochroic properties, which is an optical phenomenon. Depending on which angle the mineral is inspected, the color of it differs. On the x optical axis, the mineral could be seen in a pale blue color; on the y and z axis, the mineral's color changes to blue. It has tabular crystals and sheaflike or irregular aggregates.^[2] Lautenthalite is associated with wroewolfeite, which it tends to overgrow. It is also associated with anglesite, devilline–serpierite, galena, linarite, brochantite and schulenbergite.^[3] It forms small singular crystals with a size of up to 0.5 × 0.3 × 0.03 mm.^[4]

Lautenthalite
General
Category	Mineral
Formula (repeating unit)	PbCu4(SO4)2(OH)6 · 3H2O
IMA symbol	Lth[1]
Strunz classification	07.DE.70
Dana classification	31.06.01.02
Crystal system	Monoclinic
Crystal class	Prismatic H-M symbol: (2/m)
Space group	P21/b
Unit cell	2,799.47
Identification
Color	Blue green, green, greenish blue
Twinning	Polysynthetic on {100}
Cleavage	Good on {001} and {010}, distinct
Mohs scale hardness	2.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	3.84
Density	3.84
Optical properties	Biaxial (−)
Refractive index	nα = 1.659(2) nβ = 1.703(2) nγ = 1.732(2)
Birefringence	0.073
Pleochroism	Weak
2V angle	78° – 79°
Dispersion	Strong, r < v