The operative verb in Mark 14:3 is "suntribo" which (in this instance according to BDAG) means, "to cause destruction of something by making it come apart, shatter, smash, crush; eg Mark 14:3, Matt 12:20, 5:4 Rev 2:27".
I note that Ellicott understands this to mean, "The Greek word implies not so much the breaking of the neck of the costly jar or flask, but the crushing it in its entirety with both her hands." (Bengel's Gnomen appears to agree.) However, there are several things that make me doubt this understanding.
- Barnes Notes suggests, "This may mean no more than that she broke the "seal" of the box, so that it could be poured out. Boxes of perfumes are often sealed or made fast with wax, to prevent the perfume from escaping." Cambridge commentary agrees.
- The only way that the perfume could be poured after "braking/shattering" the container would be to brake/crush it over another container, else the liquid inside would spatter everywhere and be wasted. Therefore, it is much more likely that the container either had its neck broken, or a wax seal was broken to allow the nard to be poured in an orderly fashion. In any case, having broken the vessel, it could not be resealed and had to be used all at once.
- Other uses of this same verb, "suntribo" do not necessarily require shattering, such as Matt 12:20 = "a reed that is bent/crush/bruised (etc)"; Mark 5:4 = "broken shackles".
In any case, the import of this part of the story is that the perfume was very expensive and was part of Jesus anointing for burial. Further, the fact that it was very expensive and was purchased in a non-resealable container meant that it could NOT be partly used and some saved for later - all had to be used immediately. A wonderful metaphor for the woman's generous gift to Jesus.