Rhodium was abundant inside the valley of crystals , however usually they were small Crystal's, the size of a palm. What Rudra needed was a rarer type of Rhodium deposit , that was as big as a house. It typically needed 40 years to build up , and would only be found at places with abundant mana. Hence why the nocturnal worms were also found near it.
Even after 2 days of looking for it , no clues were found and the party members started to get anxious , the valley of crystals was big , but that big that it could not be completely scouted in 2 days time.
However what even proffesional miners could not find , was found by heaven's son Karna , accidentally at that. While bored Karna decided to spar with Neatwit for a while , and in the intense battle he needed to rely on mind's eyes. When he activated it though , he could percieve the terrain around him differently , as he located the rhodium deposit!!!
