Copper Sulfate
"There have been reports of human suicide resulting from the ingestion of gram quantities of this material"
Malachite poisoning?
"After a couple of hours I also noticed that I was becoming short of breath, rather 'chesty', coughing and my nose was running. .. I have since checked the Internet and found that there has been other cases of Malachite or Copper sulphate poisoning"
@TexieLouWho21 welcome! These two sources explain that malachite poisoning is also called copper sulfate poisoning; provide the fatal dose for copper sulfate poisoning and describe the symptoms of it. Those symptoms include a heavy cough and vomiting. These are symptoms that Tammy Daybell was described (IIRC described by Chad) as having demonstrated the night she died: that she went to bed with a bad cough, coughed so hard that she vomited and then when Chad woke up she was dead and had fallen out of bed. MOO
@TexieLouWho21 you have identified a potential poisoning agent for the theory that Chad poisoned Tammy.
So the malachite ring purchase
1. Allowed KW to find out where to send LE for a welfare check on the kids
2. Provides possible evidence that Chad and Lori were planning to marry while Tammy was still alive (ie premeditation to kill her)
3. Offers a clue to the method for killing her (copper sulfate poisoning)
And it seems to me like the kind of out there mystical thing that appeals to this crowd.
Edit to add quotes and that all of the above is IMO