The greener it is, the softer it is according to an article on HOUZZ.

My soapstone is green and it is very soft - so as you can see from the responses, there is a lot of variability - shop around and ask your fabricator or stone distributor about the relative hardness of the slabs they sell.

Lets not confuse Hardness with Density. Soapstone is the densest natural stone, but on the other hand, is very soft. What might have broke the blade is the density of the stone.
Soapstone will vary from green to dark gray (almost black). There are some soapstones in the market that come with no green whatsoever. And it is true that the darker the soapstone, the harder it is because less amount of talc the stone will have.
Check our website http://www.stonecenteratlanta.com/#!soapstone-gallery/c1blb for different types of soapstone.
Do not hesitate to ask if you have any questions.

Is it true that mineral oil is used to 'seal' the soapstone? And the 'grey' will become very dark once oiled, almost black? Is all soapstone 'honed' finish or is it available polished?

innercalm,
There are different colors of soapstone, going from light gray to dark gray. It is true that once applied the oil or wax the soapstone will get a much darker tonality.
The mineral oil won't seal the soapstone. What the oil, or wax does is to darken up the stone evenly. If you don't apply a mineral oil to it, the soapstone will darken up on the higher traffic areas such as oven, cooktop and sink, so the application of the oil or wax, is just to give an even look throughout the countertop.
You should not apply sealer to soapstone since it won't penetrate into the stone.

My kitchen is being remodeled. I chose grey. They applied the mineral oil and now it is black. What can I do? It does not go with my backsplash or anything else.

If you wait awhile, the oil should disappear & the gray should return.

The oil does not impart a permanent color change. As a matter of fact if you want the deeper color that mineral oil produces, you have to reapply every so often. While your stone may not fade to the original chalky grey that it was when installed, it will definitely fade back to grey over time.

Seems like the question was not really answered. Does ALL soapstone have green hues and green veins? I ordered grey with whit veins and was told it turn black with oil. The veins turned green and the grey turned darker with green specks. Was I mislead when I was told it would turn black with the veins white? Yes I can stop oiling and it will turn back to grey but I like the oil look. What to do?

Yes, the original question was answered regarding green: go back and read Stone Center's 1st response.

Stone center, can soapstone be stained/sealed to minimize the color enhancement of free? Is is food safe and can it resist heat if sealed/stained?

Yes you were misled about your soapstone. It will always be green. I have that type. The black with white veins is a different soapstone type.