Coral brings calcium carbonate to the soil. Calcium is needed by the microbes and plants. The most commonly known affect for garden plants when calcium is deficient is cat facing on tomatoes. But there are plenty of other problems that veggies can suffer from low calcium.
Calcium carbonate also has an effect upon soil pH. Since I have lived with acidic rain and air for years now, my soil tends to be too acidic for most veggies to grow well. Coral sand helps moderate pH.
Also, I don't wash the sand prior to using, so micro amounts of ocean minerals are clinging to the coral.
Heated coral chunks
The only difference between this a coral sand is the size of the pieces. I don't know if the heating has any effect upon the calcium availability. The reason I heat the coral chunks in a fire is so they are easily broken up. Sometimes I can hand crush the coral into smaller pieces. Other times I need to use a hammer or have my truck run over the chunks to break them up.
Why use chunky coral? It helps with drainage in heavy soils. And I suspect it allows for a longer period of availability....that is, the calcium carbonate lasts longer allowing for less frequent applications.
I use this for mineralization purposes. Some of my garden beds are mainly organic material with not enough rocks. The lava sand provides the minerals in lieu of rocks.
I don't use much ocean water, just a sprinkling. It adds some micro nutrients not otherwise readily available via the organic material I use to make compost. Keep in mind that if the micro elements are lacking in my soil, they won't magically appear in my weeds I dump into the compost bins. They have to come from off the farm. Ocean water helps with this. But it is used sparingly.
While bone contains calcium, it also contains phosphorous. My soil was low in phosphorous when I started out. And since it was also very low in calcium, bone seemed like a good choice. Around here, bones are very available. I can gather a pickup truck load in less that 30 minutes, anytime I need them. One just needs to be in the good side of the right rancher and know the right locations.
Why burn it? To make it easier to break up. When processed by fire, the bone readily crumbles.
Wood ash increase soil pH faster than calcium. And since I live in an acidic environment, wood ash is a good choice for me. Ash is also a really good source of potassium, another element that my soil needed when I started up. I use wood ash lightly in the compost bins. But I also use it as a dusting on specific garden beds that test lower in pH than others.
I initially started to experiment with biochar years ago. Personally I haven't seen the results that the hype predicted. But then, my soil isn't in as poor condition as a lot of other soils. But I have seen the useage of biochar improve my soil tilth. Where I've used biochar the soil seems lighter, a little easier to work, and drains better. Having my soil absorb water but also drain productively is important to my food growing. I feel that biochar has had a positive bearing on that.
I have a patch along the bank of a dead river bed on my land that is dirty volcanic cinder. Most likely brought down the mountain during heavy rain events. I like adding a bit of this cinder to the compost. It helps with drainage. But being full of holes like a sponge, it also retains soil nutrients and moisture. Plus it provides footing for plant roots.
Feathers & Fur/Hair
Feathers and fur provide not only nitrogen, but also many micro amounts of assorted minerals. One benefit to using them that I like is that they are slow to breakdown. So it's like using a slow release nutrient. When I use my compost, if I look carefully I still identify feathers and fur. That's fine with me. The soil microbes will use them gradually over time.
Why fruit specifically? Basically for the sugar content. Some people purposely apply sugar or molasses. I use waste fruit because it is so readily available here. I really don't know if the addition of sugars really improves soil microbe numbers, but I haven't found it to be a detriment. So since I have access to waste fruits often throughout the year, I use them on a regular basis. The goal is to produce a very large population of soil microbes in the compost.
The rest of my compost ingredients I don'tclassify as amendments per se. They are a hodgepodge of plant and animal materials. They are the essence of compost. What I consider to be amendments are materials that are not routinely found in compost but have a significant bearing upon the soil.