I used to collect crystals and rocks - yes there are straight lines in nature even squares in rock formations.
Petrified wood as you may know is the displacement of the original "mold form" (wood in this case) with minerals - most crystalized quarts but it can mean any type and most are a composite. This happens in different ways.
Ores and Irons, chromium, mercury, arsenic and many more (iron ore which is very common and can range from a darker brown to bright red orange) can be found in petrified wood and as with any rock one uses with fish these minerals can range from safe to toxic (over time even if it did not leach something obvious as it is now). PS. Bleach can be neutralized with vinegar but if you boil a rock it will kill any pathogens. Heavy metal poisoning can be rapid or a slow chronic death.
I took geology classes a long long time again but much is now online.
There can be copper, chromium and other heavy metals - we all need x amount (very very tiny micro amounts and from natural sources - as do fish) but unless you can test the water for specifics (see the test kit at the link below) you would need a RO filter to make sure it is if it does leach these toxic heavy metals. Here is a link from Dr. Fosters and Smith.
Another link on sources of heavy metals in aquarium water.
"Metal ore in the rocks you've added to the tank."
Power washing won't get rid of any leaching of toxic minerals. (note coal in the following link)
A decorative type of fossil wood where the original organic material has been replaced - usually by chalcedony or agate (cryptocrystalline quartz), but sometimes by opal, coal, pyrite, calcite and others.
Colors red and green are usually caused by iron, but a few of the more brightly colored green woods may be colored by chromium.
Here is a post from another Aquarium forum (from a long list I used to have).
It depends on what the replacement rock is. If it's limestone, yes it will change the pH of the water--it'll make it more basic. If it's agate, it won't.
Try submerging it in vinegar and see if it effervesces (produces bubbles). If it does, it's likely limestone or carbonate-bearing, and will change the pH (it'll make the water more basic). In that case, I don't advise putting it in a tank with your fish, freshwater or salt.
Whether it's carbonate-bearing or not, you should rinse the piece in clean water after the vinegar test.
Agate, jasper, or quartz varieties (crystalline or chalcedony, for instance) are probably safe enough, although as with anything else you want to introduce to your tank you should immerse the rock in clean water for a few days or a week first to remove soluble contaminants. If the water after a few days is visibly discolored or has an odor, soak it again until the end bath is clean.
The main concern I'd have would be whether it contains toxic compounds. Some minerals contain mercury or arsenic, for example. While all of the petrified wood I've seen in person has been some form of agate, jasper, or quartz, there are other minerals such as hematite that can form replacement fossils. Sandstone is porous and could include toxic compounds. You really want to be sure of what you're putting into the tank before exposing your fish.
For me - too many "ifs" to risk it.