synadelphite

\\ˌsinəˈdelˌfīt\ noun (-s)

Etymology: German synadelphit, from Greek synadelphos one that has a brother or sister (from syn- + adelphos brother) + German -it -ite — more at -adelphous

: a mineral (Mn,Mg,Ca,Pb)(AsO₄)(OH)₅ composed of a basic arsenate of manganese often with other elements (as magnesium, calcium, lead) and occurring in black prismatic crystals and grains (hardness 4.5, specific gravity 3.5)

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synadelphite /sin-ə-delˈfīt/ (mineralogy)

noun

A manganese aluminium arsenate

ORIGIN: Gr syn with, and adelphos brother, as found along with similar minerals

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synadelphite Min.

(sɪnəˈdɛlfaɪt)

[ad. G. synadelphit (Sjögren, 1884), f. Gr. σύν syn-¹ + ἀδελϕός brother + -it, -ite¹: so named ‘because intimately associated with other related species’ (Dana).]

An arsenate of manganese and aluminium, with some calcium and magnesium, occurring in black or brownish-black monoclinic crystals.

Dana Syst. Min. 801.