Can lava rock create ammonia spikes?

[Red_Belly_Pacu]

I bought a used tru vu plexi 55 gallon fish tank. The person selling it sold it to me with very large lava rocks. Well I put the lava rock in my other tanks and there was an ammonia spike. Was wondering, how can lava rocks cause an ammonia spike if that is the case?

 

[KaiserSousay]

Just a guess, but they could have been packed full of organic debris from the old tank.