
1) Mineral 2) Mineral tar 
Found on 
https://www.crosswordclues.com/clue/maltha

thick mineral pitch
Found on 
http://phrontistery.info/m.html

• (n.) A variety of bitumen, viscid and tenacious, like pitch, unctuous to the touch, and exhaling a bituminous odor. • (n.) Mortar.
Found on 
http://thinkexist.com/dictionary/meaning/maltha/
 Mal'tha
Mal'tha (măl'thȧ) 
 noun [ Latin , from Greek 
 ma`lqa .] 
 1.  A variety of bitumen, viscid and tenacious, like pitch, unctuous to the touch, and exhaling a bituminous odor.  
 2.  Mortar. [ Obsolete] 
 Holland. Found on 
http://www.encyclo.co.uk/webster/M/14

Maltha is a variety of bitumen, viscid and tenacious, like pitch. It is unctuous to the touch, and exhales a bituminous odour.
Found on 
http://www.probertencyclopaedia.com/browse/GM.HTM

[
n] - a thick black tar intermediate between petroleum and asphalt
Found on 
http://www.webdictionary.co.uk/definition.php?query=maltha
 mineral tar noun
mineral tar noun a thick black tar intermediate between petroleum and asphalt
Found on 
https://www.encyclo.co.uk/local/20974
  No exact match found.