dickite

{{infobox mineral | name = Dickite | category = Phyllosilicate minerals | group = Kaolinite-Serpentine group, kaolinite subgroup | boxwidth = | image = Dickite-d06-179a.jpg | alt = | caption = | formula = | IMAsymbol = Dck | molweight = | strunz = 9.ED.05 | dana = 71.01.01.01 | system = Monoclinic | class = Domatic (m) (same H-M symbol) | symmetry = Cc | unit cell = a = 5.150, b = 8.940 c = 14.424 [Å]; β = 96.8°; Z = 4 | color = White, with coloration from impurities | colour = | habit = Pseudohexagonal crystals, aggregates of platelets and compact massive | twinning = | cleavage = Perfect on {001} | fracture = | tenacity = Flexible but inelastic | mohs = 1.5–2 | luster = Satiny to pearly | streak = White | diaphaneity = Transparent | gravity = 2.6 | density = | polish = | opticalprop = Biaxial (+) | refractive = nα = 1.561 – 1.564 nβ = 1.561 – 1.566 nγ = 1.566 – 1.570 | birefringence = δ = 0.005 – 0.006 | pleochroism = | 2V = Measured: 50° to 80° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }}

Dickite () is a phyllosilicate clay mineral named after the metallurgical chemist Allan Brugh Dick, who first described it. It is chemically composed of 20.90% aluminium, 21.76% silicon, 1.56% hydrogen and 55.78% oxygen. It has the same composition as kaolinite, nacrite, and halloysite, but with a different crystal structure (polymorph). Dickite sometimes contains impurities such as titanium, iron, magnesium, calcium, sodium and potassium.